Guilt and I

I haven't yet decided whether this makes me a bad person or not but I rarely feel guilty for doing the things that I do. Yes, I am a cheater. Yes, I cheat with married men. Yes, I have fallen in love with a woman's husband. I work with young adults and I often tell them that what you do, the actions that you take, those don't define who you are. I use that when they come to me with a mistake that they have made or something they feel guilty about. By that logic, I shouldn't define myself as a "bad" or "evil" person because of my adulterous secrets. 

Usually, this rationalization works really well and the guilt rarely lasts. 

However, I have been having more difficulty rationalizing with myself that what I am doing with A. isn't wrong. A. is going out of town for a few days which is a break that I will use as a mental health pause. A's wife is pregnant. They are having a child. This should be a happy and special time for them as a couple and as a family. I feel guilty. For the first time. I feel badly for her. A. always tells me that I shouldn't feel guilty because if he were not doing this with me, he would be doing it with someone else and who knows what kind of person that woman would be like. When I told him yesterday that it feels as though we are unable to control and refrain ourselves, he cut me off and said: "It's not about that anymore. You know what this is. It is so much more". 

A. has always been a cheater. I haven't figured out whether that is because he married the wrong woman or whether monogamy is simply not possible for him. He cheated before getting married, told himself that he would get a divorce two months in his marriage, had an affair, was about to leave his wife when she announced that she was pregnant, continued the affair, confessed and lost both his wife and lover, eventually got back in his marriage and continued having serial affairs. It is so difficult for me to reconcile what A. does (which sounds terrible when he tells me  about his life and even more terrible having written it out) with who A. is. Or at least, with who A. is to me. 

He is the most passionate, kind, loving, open man I have ever loved. He is a wonderful friend, father and lover to me. But he is an awful husband. 

A. doesn't feel guilt. He feels that he married too young, that he shouldn't have married at all and that his wife is a terrible match for him. Yet, he stays. Despite getting married over a decade ago and thinking the marriage to be temporary, there he is, still with her. Despite knowing her husband and part of his history, she prefers to keep the marriage together as well. 

Should we live unhappily in order not to hurt the ones around us? 

Are we inherently bad if we act a little selfish sometimes in order not to miss out on experiences such as love and passion?