Why would a married man be jealous over his other woman?

[Dtownguy]

I am trying to understand my friend. He says he is happily married but has been having a sexual relationship with a single woman 15 yrs younger than him. It has been going on for half his marriage. He say the OW is just sex. I told him 7 yrs can't be only sex. He said for them it is. The problem is that he acts so jealous regarding her. I met her and she is a wonderful woman. The type not meant to be a side chick. I told him this and he accused me of wanting to **** her. He is always accusing her of cheating and stops by her place unannounced to "catch her cheating ". I have never cheated so i can't understand him. It is effecting our friendship because he thinks I want her. I try to talk to him but I don't think he's being honest about his feelings for her. Am I looking to much into it? I just think if I knew why he acts like that I would know how to handle the situation. Is it love or possessiveness? I don't want to lose a friend

[DrReplyInRhymes]

He's probably projecting,

His own problems reflecting,

A broken conscience I'm detecting,

No love but jealousy, quite perplexing.