I need some advice on what to do, my ex (18) and I (21) broke things off a couple of days ago at a fire in my backyard. We were together for 3 years, towards the end of the relationship, I started to get a gut feeling that my ex was cheating or possibly finding my replacement. There were these two guys that she was talking to, Josh and Mitch. I was getting a funny feeling about these two guys. After getting introduced to them on separate days from one another. After seeing these guys and hearing them flirt with my ex and her flirt back, I got too uncomfortable, I tried to express this to my ex, but all she said was that "they were friends and nothing more". Well later It started to get to be too much, I started to overthink a lot and even started to fall into a battle with depression. My ex stopped hanging out with Josh and started to hang out a lot with Mitch, they started to go to parties, bars, concerts, and even late-night drives. I started to distance myself and just focused on hanging out with friends and work since she was always "busy". This was happening in the last 2 months of our relationship. Fast-forward to the fire, it was only her and I, we were having fun drinking and just talking.  we did this for about 4 hours, the fire was dying, and she started to go on her phone more often.  I asked if she wanted me to bring her home (I was sober) but she responded with a quick "no", I then offered her to stay the night, but she refused, then I asked if she has a driver that can pick her up like a family friend that the family knows and trust. She then lists off a bunch of family friends, then she got quiet and said, Mitch. I was confused because Mitch doesn't have a vehicle, so I started to ask questions because I was confused. Then the news broke, Mitch was at my Ex's house, in her room, waiting for her. I just remember falling silent, thinking how I should have trusted my gut. I wasn't sure if I should be mad or calm, After hearing that I started to pack up the chairs and alcohol, staying quiet. After that, I came back to the fire and she started crying saying "I like him" and "I have feelings for him" and I just responded with "It's alright, if he is what brings happiness into your life, go for it." It hurt saying that to someone I loved for 3 years...then she pulled the "can we be friends" card. I knew this would cause too much pain for me to watch her be happy with that guy, so I refused and explained why. She started crying again, and so did I. She then left and I was there left thinking...Let's just say I'm in a dark place right now and need guidance or just listen to what people have to say.