Cheating boyfriend ...

So me and my boyfriend have gone throw a lot. We had two miscarriage we Decided to try again we have are wonderful son now he is four months. My pregnancy was so complicated. He was supported all the time. I noticed something was wrong so on Monday I checked his phone and he was texting this other girl n calling her buttercup, when he noticed what I saw he said to give him back the phone. Which I didn’t I called the number but no one answer but I know it did recorded. He got mad n snatch the phone away from me. I was bursting in tears and told him why the fk was he doing this, he had just told me that he loved me and now everything was lie. He told me, I’m not cheating that’s all I have to say I’m like so u can call anyone buttercup so that means I can call anyone babe? He just had all the guild face. Don’t know what to do I’m so just overwhelm. I work and make more money then him so I know that’s not an issue. What should I do?