and really good question, BTW.  I'm very happily married and got into "play world" because my wife has a physical problem that makes intercourse painful for her.  We do a lot of other sexual stuff, she is really open and willing and we have fun, but not to the frequency I prefer (and I like good ol' fashioned headboard banging fucking too).  I was getting frustrated and it was affecting our relationship.  There was some insinuation by my wife that I should "do what I have to do" for my sexual fulfillment.  Mind you, this is not discussed at the kitchen table or anything.  I keep it utr and discrete, and it's not discussed.  (Although, I've really cut back the last 6 months or so after being pretty active for about 3 years--I think it might be a somewhat natural aging factor of less interest in sex generally).

Anyway, I got the aggressive fucking that I wanted (to the dismay, I'm sure, of some lady friends, but what the hell, I'm paying them for MY fantasy), at the frequency I wanted it (the misses has no clue how frequent it was at times), and it really released the tension at home.  I wasn't constantly frustrated with my wife anymore and when the mood hits us, it isn't forced or negative because of things I can't do with her.  I've even brought some things to our sex life I was able to hone with playmates, that might have been more awkward initiating at home.  My hobby experience was a real win-win for me.  Kept my marriage together and allowed me to relive my college days again.