My boyfriend has betrayed me?

i have a boyfriend, we have a kid together. of late, he has really changed! he talks to me rudely, use abusive words and just reacts to me like his immediate enemy. i wanted to know why all this is happening, and luckyly found out that he is having a relationship. i asked him but he said that she is just a friend, and i as well contacted the lady and she said likewise. i am really torn apart,cos i had future plans with this guy but now he has really hurted me , betrayed me. oh, we have a distant relationship, but despite all that, i thought i could trust him! what should i do?