Not sure why, but I do feel great or sexually aroused knowing that the partner i was fucking is someone gf/wife or even mistress.
In fact, sex with wife or mistress is so much better as they are more sexperienced and willing to accommodate. So much more fun and usually, they know how to take care as not to get pregnant or they already have femaleDom inside them.
Over my life, I had my fair share of fucking gf/wivies and mistress. So good memories, which will accompany till my death bed. LOL.
The only word of caution : dun keep too long term, engage, enjoy a few times, then move on.
The longer you keep, the higher chance of problem you get.