The relationships go well for a couple of years, then i find out thru mutual friends that the guys have been cheating on me for a long time. I've been with my boyfriend for 4 years. A year ago he slept with a good friend of mine. I found out thru a 3rd party, and decided to stay with him. After a year, the emotions are still fresh. Dr. Ruth, i don’t think i could ever trust another male again. Should i continue with this relationship, and try to deal with it? How can i regain my trust in people?

People make mistakes. It’s possible that your boyfriend did exactly that, though that he chose to do it with a friend of yours makes me doubtful. But lets step away from the immediate problem and look at the bigger picture. You don’t say how many men have cheated on you, but it does seem that you don’t have the knack for finding the right men. So here’s my question to you: What have your friends said about these men? If they’ve been warning you all along that you are not good at picking men and you’ve not been listening to them, then what I would suggest you do in this case is to ask your friends what they think. If they, in general, think your boyfriend is not right for you, then leave him.
Of course maybe you’ve just had a run of bad luck. That could happen. If your friends are as surprised at what’s been happening to you as you are, and your boyfriend hasn’t given you any signs that he’s been cheating, and you really do love him, then try to stick it out. If you need the help of a therapist, then go get the help you need.
There is no one right answer to your question. I often tell people to trust their gut instinct, but yours may not be in working order. So seek some outside opinion, and then decide what to do.