Help, I need advice please

So I was looking through my bfs phone, because I heard one of his friends was hurt. So I wanted to help and went to find a message saying

"Do you honestly think I'm happy

I'm not

I'm with a girl that threatened to take my child away

I keep wanting to tell her I want to break up but I cant"

Okay yes I made a mistake by saying I would take his child away, but since then I have showed him I didn't mean it.

Point is, is that at first he said it was out of anger he said that and he felt so bad. He said we had a fight that day and that's why he was angry. He tried to make it up to me, but now I found out he lied to me. The day that he sent that, was a day I went out of town to see my brother. That day he was very happy, and made it seem like he was.

I don't know what to do anymore. I'm a full time mom, I am going to college, and I'm working, because he isnt. I live with him and his grandma who makes me very unhappy, and insults me. I hate living in this house, but I do because of him, because I want to be with him. To just find that message and now find out he lied to me even more, breaks my heart, and makes me think this entire relationship has been a lie.

So if you have any advice, please help, I'm desperate.