I guess this might be TMI, but...
When WS and I first got together, he was interested in some stuff that I thought signaled that maybe he was bi or gay. He told me they were things that his ex (a woman) used to do to him and he was interested in doing things to me that weren't going to happen.
Before we got married I told him that if he had to go out and experience these things or it would make him unhappy in some way, he should tell me now. He told me he could live without. I told him we could revisit his interest in those things down the road, perhaps. But I couldn't promise I'd ever do them.
Occasionally if we fooled around after I'd had a few drinks at a party or whatnot, he might get away with a little more in those areas (literally)... but, generally, he respected my parameters.
So when he first told me he had had an A, I almost expected it to be with a man. Or, let's just say, I wouldn't have been caught off guard by that.
Frankly, that it was with another woman sort of surprised me. Not that I really did think he was bi or gay-- but just that I didn't see him finding sex with a different woman all that compelling.
I came to find out that she let him do things that he never told me he wanted to do-- basically some S&M stuff. He had tried some of those things out on me the last time we were together out of the blue and I was so miserable with it, I told him we had to stop. Actually, on DDay, when he told me he had an A, the first thing out of my mouth was "What the hell was THAT?!?!" in reference to our last time in bed together. I basically came out and accused him of sexually assaulting me, now that I know it wasn't just him "out of practice" because we hadn't seen each other in a few months. 
That last experience was so miserable that, if that's what they are doing together, she can have him.
