How to React to a Friend Who Flirts with Your Spouse
It's natural to be angry or upset if your friend flirts with your spouse, but you can handle the situation by calmly communicating how you feel. If your friend starts flirting with your spouse in front of you, put your arm around your spouse or hold their hand to remind your friend that you're together. If they continue, just walk away from the situation with your spouse as soon as possible. Then, you can ask your partner in private what they thought about your friend's attitude. If your spouse thinks the behavior was inappropriate, have a word with your friend in private the next time you see them. Say something like, “I'm sure you mean well, but it seemed like you were a little too friendly with my wife last time we met and I'd appreciate it if you toned that down.”
Demonstrate affection for your partner. If you're concerned that a friend is flirting with your spouse, move near your partner (even if you're across the room) and make a physical or verbal demonstrative gesture. For example, you could put your arm around your partner, tousle their hair with your hand, sit on their lap (if appropriate given the context), or give them a kiss. This demonstrative affection will make you seem calm and confident, even if you feel jealous or insecure internally. Make a joke or comment to diffuse the situation. This will be useful if your friend is unaware that their behavior seems flirtatious, and to communicate to your spouse that you don't necessarily approve of the friend's actions. If your friend is intentionally flirting, your comment can serve as a warning or “back off” signal, making clear that you don't appreciate their advances toward your spouse. Say something like: “Hey this is my spouse, go find one of your own!” “We'll have to find you a girlfriend or boyfriend of your own, buddy.” Remove yourself and your partner from the situation. If your friend continues their flirtatious behavior, even while you're close at hand, it may be time to leave the situation before you become angry or the flirtation becomes more serious. If your spouse appears to be enjoying the flirtatious attention from your friend and even returns the behavior, it's best to remove you and your partner from the situation, whether it's a dinner party, happy hour at a bar, or an evening out on the town. Even if you're angry at this point, avoid taking it out on the friend or your spouse before you've had a chance to discuss what happened. Take time to process your emotions. It's important that you acknowledge—both to your spouse and to yourself—that you're upset over what happened. It would be wise to acknowledge these feelings before expressing any anger towards your spouse or towards your friend. Give yourself time to decide if you are truly offended by your friend's actions or you were only annoyed in the moment. If you process emotions best by thinking through the event and considering the various responses you could have, take a long walk to give yourself time to think. Be sure to consider if there is a pattern. For example, does this sort of thing happen often, or has it ever happened before? Do you often feel jealous? Ask your partner if they noticed the flirting. Before you make any assumptions about your spouse's response to your friend's behavior, find out if they thought your friend was being deliberately flirtatious, or just being friendly. Sometimes kindness, polite conversation, and friendly attention can be mis-construed as flirting. Say something like, “I noticed that Ben stayed near you at the bar yesterday and didn't seem interested in talking to other people. Do you think he was flirting or just being friendly?” You should have this conversation relatively soon after the flirting occurred. It will do you little good to wait a month before bringing up the incident. Acknowledge your jealousy or frustration to your partner. Married partners should be emotionally transparent with one another, and this situation certainly calls for transparency. In this situation, you need to help your partner understand your emotions, and bottling up your feelings of frustration won't help. You don't need to be petty or sarcastic; rather, help your partner understand why the flirting bothers you. Say something like: “I think that Steve was flirting with you last night; it made me feel like you enjoy talking to him more than to me, and I couldn't help but wonder if you enjoyed the flirtation.” “It made me jealous to see Jess flirt with you at the party; I don't like it when other people speak to you like that.” Do not blame your partner for the friend’s flirting. Unless your spouse was clearly enjoying the flirting and even flirting back, don't blame him or her for having encouraged the attention, as this was likely not the case. Also, if you blame your partner, they will likely react with hostility and may accuse you of prying or being overly sensitive, which will stop productive conversation. You can clarify this by saying, “I know you didn't ask to be flirted with, and no part of it is your fault.” However, if your spouse becomes defensive or evasive, that is also information. Sometimes flirting can indicate that someone is cheating. Clarify boundaries for both you and your spouse. This should be a healthy and productive conversation for both you and your partner, in which you can clarify what you do and do not find acceptable concerning behavior that seems like flirting with other people. The line between flirting and normal social behavior can be thin, so you and your spouse should name specific actions that are either acceptable or too far—and make it clear that any sexually suggestive behavior or comments from other people are inappropriate. Say something like: “Of course friends can hug each other, but it concerns me when other men put their arm around your waist.” “You and Cindy seemed to be sharing a lot of inside jokes last night after the movie, and didn't spend time conversing with anyone else. That makes it seem like you're flirting with her.” You can use this as an opportunity to make a list of boundaries that are important for each of you in the relationship. Talk with your friend about the incident. It's best to talk with your friend directly, rather than making dramatic assumptions about their behavior. Reach out and explain that you'd like to have a conversation in the near future; for example, you could ask your friend to meet you for a coffee. Avoid lashing out in anger or frustration as soon as you see your friend; stay calm and avoid making accusations. Say something like: “I consider you to be a good friend and want to keep our friendship, but at the movies last week I thought you may have been flirting with my spouse, and that concerns me.” Make sure that you talk with your spouse first. Don't talk with your friend before that. Ask your friend about their intentions. This should be done politely, and in a private space. Assuming that you value the friend and want to keep that relationship, you should not confront them aggressively or with hostility. Instead, have an attitude of concerned curiosity; mention the specific behaviors that you took to be flirting, explain that this upset you, and ask your friend to explain themselves. For example, say: “It seemed to me like you were flirting with Sharon at the party yesterday, when you kissed her cheek after dinner. That bothered me. Can you explain why you did that?” Ask your friend to stop the behavior. If you're not satisfied by your friend's explanation of their flirtatious behavior, make it clear that you'd like them to stop this kind of interaction with your spouse. Explain your reasoning and clarify the specific types of behaviors (joking, physical contact, etc.) that you find objectionable. The friend should respect your wishes. Say something like: “Even if you're not intentionally flirting, it still comes across that way to me and I'd appreciate it if you back off a little.” 
Demonstrate affection for your partner. Make a joke or comment to diffuse the situation. Remove yourself and your partner from the situation. Take time to process your emotions. Ask your partner if they noticed the flirting. Acknowledge your jealousy or frustration to your partner. Do not blame your partner for the friend’s flirting. Clarify boundaries for both you and your spouse. Talk with your friend about the incident. Ask your friend about their intentions. Ask your friend to stop the behavior. 