Relationship: My boyfriend cheated on me with my best friend

BOYFRIEND OF 2YEARS CHEATED WITH MY FRIEND

I have been with my boyfriend for almost 2years. We’ve been friends since high school and ended up dating in college. He is very attractive and kind. He cares about me (or so I thought) and we were perfect match.

I have this friend (Sonia) we used to be close, but ever since we started college; we began to grow apart. Sonia and my boyfriend knew each other because I introduced them in a party. We have been mutual friends, but haven’t met Sonia in years.

Now this is where the problem starts. This few months I’ve been busy and I don’t feel pretty well, not only that, but my sex drive have dropped a lot. Anytime my boyfriend tries to initiate sex; I’d turn him down because I have no desire to have sex
with whosoever.

At first, he was very understanding, but then he started to get annoyed whenever I
turn him down. I finally made up my mind and asked him what his problem is. We ended up fighting and I told him that we need a break.

3 weeks later we made up and came back together again. But, for some reason I couldn’t shake the feeling that he is hiding something from me. From what I heard, him and Sonia have been hanging out together lately. I didn’t think much about it; he is free to hang out with whoever he wants.

But the thing is, Sonia has always had a crush on him. She is always very flirty towards him. Not only that, they also hooked up couple of times before we came back together.
Few weeks later I noticed that he has been getting messages from Sonia and he is acting more strange. I finally had enough and decided to look through his phone while he was asleep (I know it’s bad, but I couldn’t help it).

And I was right.
They have been hooking up with each other for months ever since our break. I felt heartbroken; had to confront him and he admitted it. He said he has needs and he’s tired of waiting. He said I should feel lucky because he didn’t hurt me. I broke up with him instantly.
2years is wasted because of Sonia, please I need an advice on how to cope with things.