My boyfriend and I have been dating for 3 1/2 years but last weekend we went out and he got drunk after I dropped him of he texted my sister saying he had feelings for her and that he's been thinking about her. I didn't find out until 2 days after when I asked him why my sister wasn't speaking to him he said I don't know. So I asked her and she at first wasn't going to tell me but then she should me the text I confronted him and broke up. He told me it was a mistake that he only loves me but I don't know if he's being honest what should I do?

Depends - will you be able to trust him again? Will you spend your time checking up on him and your sister? Will you be sneaking looks at their phones to see if they are texting each other? Will you not have him over to your house because your sister is there? Will you not invite your sister along because of looks that might happen or worse?

If you answered yes to all or most of those questions then it won't be much of a relationship right?

If you decide to stay it is reasonable that they not have each other's phone numbers and shouldn't be texting each other.

But I know it's not my sisters fault she would never hurt me. And he says it my fault because I was very jealous not only with my sister any girl but I learned to trust him and now I don't know what to do. She said she can't see him the same way anymore because she trusted and looked up to him

He's lying to you. Being drunk wouldn't make him do something like that if he wasn't already thinking it to begin with. Being drunk merely gave him the nerve to act on it. You need to ask yourself this... if he did that with your sister, who else is he doing it with?

You are better off without him.