My Dilemma

An old fuck buddy of mine has recently contacted me and offered to take me to a swingers club. It's like he pyschically knows that

a) it's been a while and I am gagging for it
b) I am pre-menstrual and absolutely gagging for it
c) it's that time of year (cold, dark, festive bollocks) and I am definitely gagging for it
d) I have been waiting for the chance to swing with someone who is open-minded like me and I am literally gagging for it

Now, he's not the greatest fuck in the world, but then he's not terrible either. I suppose I feel neither here nor there about shagging him. He's not the most handsome man, nor the largest - in every sense - which doesn't make him that appealing to me, but, he is a sex-mad dirty fiend with a wicked glint in his eye and it is this about him that gets me off. But I still feel uneasy about fucking him again.

It's not that his technique is all bad: when he fucks me from behind and I ask him to spank me, he knows where, and just how hard - he takes direction very well. Plus, for a small man, he is surprisingly strong, and has thrown me on the bed, pushed my legs above his head and rammed me as hard as I could take it, more than a few times. And even with his size, he knows how to make me feel all 'girly' and submissive, telling me

"You like my cock in you don't you? You dirty little girl, move those legs up, I am gonna fuck you hard now"

which of course he does, mixing in a few slaps on my arse or thighs to spice it up.

No, it's not the sex that's the problem. It's the situation. He has a partner. And I've met her. And she's very nice too. But she's not into swinging. I tried to suggest ways that he could convince her that going to a sauna would be in her best interest, but he said there was no way she would even consider it. And practically begged me to accompany him.

So, here I am, faced with
a) good sex (and I am gagging for it, in case you had forgotten)
b) the chance to swing

and I am at a crossroads. Do I take him up on the offer and think only of my pleasure (ok, and his, but that goes without saying) or do I take into account that someone else could get hurt here? I know that he has always cheated on his partners - this would be no different - except I know her. How much of a feminist can I be if I am even considering fucking another woman's man? Just because he is a whore, it doesn't mean I have to behave like one too - does it?