My partner is a very sociable and outgoing person, he could be typified as the class clown - often putting himself down to get laughs out of others. He has been this way for as long as I have known him (17 years). As we have gotten older and friend groups become smaller or more distanced, every few months or so he becomes extremely down and states that he has “no friends” and that no one ever reaches out to him. I know this is not the case, I think he usually just projects his own social anxiety onto others and to be honest has unrealistic expectations of what adult friendships look like. He will get angry and frustrated and basically becomes really judgemental, often blaming the place where we live (our home state which we returned to last year after living interstate for 4 years) and that if he were back with his other friends it would be different… however he does this wherever we are - the grass is always greener. I really struggle to support him, or know what to say when he gets like this because I feel like it’s being rude to our/his friends who really do care about him, but just have other shit going on in their life - it’s really exhausting! When he is like this he cannot hear/see reality. Has anyone else been in this position? Any advise on how to best support him without just agreeing with his version of reality? 
If I even slightly challenge his thinking he gets upset and accuses me of not being on his side. 

The cycle ends when he ends up catching up/going out with friends and it’s like nothing happened!!