I made a huge mistake with my ex!?

My boyfriend had broken up with me a week before I found out that he was crushing on another girl while he was seeing me. I was so mad at him because: 1. He PROMISED me he wasn't anything like that. and 2. After we broke up we promised to still be friends. I was so mad, when I saw him next, i told him i hated him and started bawling. He walked away really shocked. The next day, i totally regretted what I said, because even though he did that to me, i still had a crush on him because he is so sweet, we have a lot in common, and i swear to god that i love(d) him! It was his birthday yesterday, and i was going to apologize, but i couldn't get the guts to talk to him. Maybe I shouldn't apologize... WHAT SHOULD I DO???