Debbie in Ohio recently found out that the man she has lived with for 2 years and has a child with him has been talking to another woman. When she confronted him about it, he first lied, and then he finally admitted to being attracted to her. She says, "Now I don't know if I can trust him again. I love him very much and he says he loves me too, but I am afraid to trust him again. This has hurt me a lot. Why can't I believe him when he says he doesn't talk to her any more and says he loves me? Please help."
I am sorry to hear that you have been a victim of a cheating boyfriend - not uncommon in today's world where opportunities for cheating are literally a click away. We all make mistakes, however, and if this is just a one-time mistake that he has made, he deserves to be forgiven provided he is genuinely sorry about it and promises to never do it again.
Since he is the one who broke the trust, it is his responsibility to do everything that he can to rebuild the trust. And you have to let him know that in clear terms. Just sit down with him and tell him exactly how you feel. And then ask him that he has to try to do his very best to rebuild the trust; otherwise, the relationship is in jeopardy. There is absolutely no doubt that a relationship without mutual trust is doomed.
Another point that you might want to think about, though, is that why was he talking to another woman. How is your communication with him? Can he talk everything that he wants to with you? Are you a good listener? Are you open-minded enough to let him share everything that he wants to? If not, he is likely to seek another listener. In other words, you both have to learn to communicate as a couple as well and you have to ask yourself if you have not done what needed to be done to be his partner. It is entirely possible that he is just a man without values and looks forward to cheating no matter how good you are, but it will be worthwhile for you to spend some time thinking about what, if anything, you may have done wrong.
If you realize that you did not take care of yourself and did not pay attention to him, then you should work together so that both of you are happy and each other's needs are satisfied. And if you have done your best and he is just a ****, then you are wrong to love him. You may want to breakup with him and move on.