Ahhhh... the story of his deception. Crack open a beer, this is going to be a long one. We were together for over 2 years. A very sexually adventurous couple in our mid 40's. We played in the swing lifestyle. We were open to full swap, partook in a few orgies, but we always played together. No solo dates. We indulged in a lot of anal, with my being on the receiving end. To this point, we never played with his rear end, and there was never any male on male contact.  But  we gradually left the large swinger club and set up the random couple dates from craigslist. We just moved progressively away from that scene. We continued our own kinky sex life. 
At some point, things just felt off to me.  The feeling wouldn't go away. His schedule changed up slightly.. had to work on a few Saturdays which was unusual. The feeling kept weighing on me.  One saturday he went to work. Called me later that afternoon, told me he loved me, asked about my day.. not unusual. Said he'd be home in a few hours. Called me on his way home.  Now, interesting side note, I have a bondage and discipline fantasy that he's just not into. I've tried relentlessly to get him to dominate me, he just wasn't into it. So I let it go. It's no fun if one of us is not having fun. Back to that night... as luck would have it, all the kids were gone overnight.  He surprised me with a spreader bar , porn and brought his inner Dom out to play. It was hot and I was delighted.   That damn feeling that something was off just wouldn't  go away. He had just gotten a new cell phone. One day, I picked up his old one and his email was still running off internet.  I looked at it and found nothing to be alarmed about. I berated myself for being an idiot. Then I hit the trash. Holy shit!! I found emails where he contacted a gay male massage therapist.  I read their back and forth conversations. He mentioned his curiosity,  how he wanted to be fully naked.  How he would be coming from work and wanted a shower before they started. The guy assured him that he was very experienced with curious males. I can't quite remember everything said because I was literally sick. I looked at the date and time of the meet and saw red. He called me to tell me he loved me while he was driving there.  And delivered the sex  I've been begging for,  after deceiving me. I was pissed and I was scared.  I could barely contain myself until he came home from work that evening.  I flat out asked him if he was cheating on me. He said no. I told him I didn't believe him and he said he'd prove it.. i could look through his phone. I told him to open his email and he did, scrolling through it in my face... then i said open the trash folder.  I can't begin to imagine what he felt when he saw those emails!! I knew he was sorry. I asked hard and hurtful questions.  I asked how he ever expected me to trust him again.  He said he hid it because he was ashamed. I get that. He said people always made joking gay comments to/ about him and he was scared. He had to find out. I asked him if he found out he liked it, was he going to continue to lie and cheat or blindside me by leaving me?  He felt every ounce of my rage. He said he didn't like it.  I read the gay massage guy's follow up email, and his response to him, telling him he really enjoyed his touch, back to him aloud. He said he was just telling him what he wanted to hear. I call BS! If he had no interest, why even reply, let alone blow sunshine up the guys ass. That smacked of someone not wanting to burn a bridge. I still don't believe that he didn't enjoy it. He refuses to share details, just says he finished him off with a hand job. His refusal to share or talk about it, makes me think much more took place. This was 8 years ago. It still creeps up on me sometimes.  As I said, i went a little crazy seeking to understand. He was awesome pledging his unfailing fidelity. But he shut me down when i needed to talk about it. He told me we needed to move past it. True to some point. But his refusal to talk about what took place, prolonged my ability to get past it. My imagination and dirty mind is legion. Is it possible nothing more happened, sure.  But not being forthcoming made me imagine much worse.  Yes I think he's hiding a lot from me, but I could also see what the fear of losing me did to him.  I spent some time researching bisexuality.  I introduced toys and exploration that focused on his pleasure.  His first prostate orgasm was the most incredible thing I've ever witnessed.  Unfortunately, he was so wrapped up in his own pleasure, he didn't return the favor. The next time we explored his backdoor with toys, I might as well not have not even been in the room. I've offered a mmf threesome, but he declines interest. I've tried exhaustively to get him to open up about his fantasies, but he will not. I've offered him the opportunity to explore the real deal with or without my presence, he declines. I just feel like he needs to keep me separate from this curiosity.  That is the deal breaker. If he explores behind my back again, it would end us. I do not believe for a minute that his "massage" convinced him that he had no interest. His exploration happened 8 years ago and I'm still struggling.