The question asker may have a personal problem with her SO, but I still think the question in the title deserves an attempt at an answer. I don’t think the question presumes that all me cheat. I think that what she doesn’t understand is how one could tell one woman you love her, and then sleep with another woman. Clearly, this behavior does not compute with her.
There are many people who are in polyamorous relationships. These people believe they can love more than one person. I believe that jealousy is an issue they have to deal with, and I have no idea how stable such relationships are. Anyway, in such a relationship, it is clear they believe they can love more than one person.
I believe there are a lot more men who think the same thing. Or, are driven to feel like they need more than one partner. Urges built into us by evolution are what drive these urges.
Clearly, some people can resist these urges (drbill) and others can’t (me). I loved my wife at the time, and love my wife now, but I was still lonely. Anyway, there’s a whole long story about it elsewhere on fluther, so I’m not going to repeat it here.
I think that other men (and women, who also have an evolutionarily driven urge to cheat) feel these urges, and many are too weak to resist them. This does not mean they don’t love their long term partners. It just means they wanted the excitement of another partner. Maybe they even want the rush of falling in love (I did.. it was my attempt to fight off some rather horrible feelings I was feeling).
I think there are many reasons why people can cheat, yet still love their long term partners. I bet I’ve barely touched the surface here. A lot of these reasons reflect problems in a relationship. Some of them reflect a different paradigm about relationships. Some of them are pathological.
Our therapist says that most relationships can be repaired if both parties come clean with each other and are honest with each. However, he’s worked with a lot of couples where the man never even admits to infidelity. People can be very forgiving if they understand what happened; what motivated the infidelity. I know I’ve been lucky to be forgiven; indeed my wife took on half the responsibility for what happened.
If you want to repair the relationship, I’d say you both have to look deeply at yourselves, and both have to own up to some responsibility. In this way, you can move to address the real problems, and, if you are successful, move forward in a relationship where there is actually trust.
If both parties don’t admit to at least some responsibility; if one person puts all the blame on the other; I think there is very little chance the relationship can be repaired. In such a case, one person is being dishonest. A lot of people prefer to play the victim because it gets them a lot of attention from others in society. Unfortunately, it also kills any chance that the relationship can be repaired. You can not afford righteousness in these situations.