To me there are three reasons why this is silly:
First, I thought it was clear that Donna was trying to get back at Stephanie by marrying Thorne...so why would anyone especially another Forrestor man get involved with her knowing that?
Second, he is taking his sons sloppy seconds...again, yuk !! Stephanie is so right when she talks about how the men in her family don't think with the head on their shoulders.
Third, he is married but it never has bothered him in the past, he has cheated on her so many times, I can't count them.