My boyfriend saw me outside getting on the bus with another guy and he automatically thinks I'm cheating so he breaks up with me. How do I handle this?

He must be insecure, and immature to jump to such conclusions, and that's not good. If he can't take your word for it, and trust you, then don't beg him, just back up and let him miss you. How old are you both?

I'm 18 and he's 24.

There's no proof he's accusing me off cheating. And there's no proof of that. I caught him talking to another guy on his phone and I talked to him about it. But he can't do the same for me... It's really hard not to think about it because it's just is... I don't know what to do, or how to feel.

I would be mad, if I were innocent of his accusations. I would be mad if my partner was so stubborn, and UNFAIR!!

Yes.

You go no contact and move on. Why be with someone who has no trust for you and will bail on your so quickly, that is not the type of boyfriend that you want.

Yes that could have been my brother or any of my family members. I think he was already cheating and that was a good time to call quits because I was with another guy the day he saw me.