Secrets always come out

So I’ve been in a relationship with my boyfriend for almost 3 years. I just got a roommate (one of my close friends for about a year now) and she moved in with me.

Backstory about my relationship - it was off and on I was smoking and he didn’t like it so he would break up with me and then I would tell him I’m done smoking and we would get back together (we were 15)

My roommate told me in a car ride that before she met me, she liked my boyfriend and my boyfriend new that. So when we would break up for an hour at a time he would text her trying to plan a date saying he was gonna be done with me for good.

This was 2 and 1/2 years ago and my whole friend group knew and never told me.

Should I be mad? I’m heartbroken about the fact that no one told me I could care less if he texted some girl to try to get over me.

What do I do? (Don’t tell me to break up with my boyfriend we were 15 at the time)

We are 18 now

She told me that after she met me she was scared to tell me because she thought I would hate her and we were becoming good friends and she really liked me. My friends don’t know that I know they know. My boyfriend is seriously regretful right now and doing everything he can do to make it up to me. He is an amazing man and treats me so well but back then our relationship was very fragile. We are so strong now and I love him with my whole heart