think?  I've found it doesn't matter what we think or even what you think, it's what the wife/girlfriend thinks that matters.  There may be some wives/girlfriends who wouldn't consider sex with an escort to be cheating because she knows you're not going to leave her for the escort.

For me, I would consider myself to be cheating.  But that's me.

By one definition you should ask yourself whether or not you could tell your GF about it.  If the answer is no, then it's cheating.

The real issue here is not cheating, it's whether you feel OK with this or not.  From what I hear you saying, you do feel fine with it, so I would say the only problem is whether or not you end up getting caught.  If you think that is a low order of probability, then so much the better.

Each of us in this hobby do a risk evaluation of what we do and then live with whatever we get.

That is life in a nutshell.

Failure on the part of anybody in a relationship to communicate what we want or need results in our having to go out and find it behind our partner's back.  While, technically, you're not cheating in the classic sense (aside from getting 'butt love' from a 'large' strap-on), you are withholding a part of yourself and engaging in behavior you feel you have to hide from your SO.  No judgement here, just making an observation.  Obviously, all of us here who are in committed relationships are in the same boat.

You initially say that there is no sexual contact and then later you say:

'...would many men admit to their girlfriend they have a fantasy about being raped by a woman with a large strap-on.'

Sounds sexual to me dude...

In any case, if you are not sharing your dom experience with your GF becasue you feel that she would either disapprove, be repulsed or perhaps hurt, then yes it is cheating.  Like someone already suggested, if you are asking and deep down you think it is then it is...

But our secrets are all that we own.

You can pump air into the bell jar
But in the end we are in there all alone.

We all keep some things from our SO. Only you can decide why you keep this info from yours. Is it because you're afraid she'll leave you if she found out? Is it because you think she's too 'innocent' to do what your dom does? Is it because you don't want to appear frail in the eyes of your SO? Lots of potential reasons. Dig in and try to find out why you can't be honest and forthright with your SO.

I hope no one assumes I'm saying that being honest and forthright is always the best policy! However, it is always good to know as much as possible about why we're hiding things.

To some cheating means having a sexual encounter with someone other than your SO (yep, that means oral sex, too).  For others, cheating goes even deeper.  It is possible to cheat on your SO by having an emotionally involved relationship with a person of the opposite sex that does not involve, and specifically excludes, your SO.  By emotionally involved relationship I don't mean a platonic friendship...although most female SO's don't really believe that their men are capable of having a platonic relationship with another woman.  They will automatically assume that something innocent WILL turn sexual.  Hence, cheating.

You are sharing an emotional relationship with this dominatrix.  It is a relationship that specifically excludes your GF.  Cheating?  Your GF might think so.

Something you said in your post intrigues me, though.  You said your fantasy has to do with something that occurred in your past.  Honestly, it sounds more like you need to visit a pshychologist and begin to deal with this event rather than spending your money on someone to continue to relive this experience.  Rape is a violent event and to continue to choose to re-live this violent event becuase something in you at the time responded to some physical stimuli is, perhaps, self-destructive.  Men do get raped, and beaten, and suffer the same psychological scarring that women do.  I'm not saying that there is anything wrong with an active fantasy life.  However, you specifically tied it to an event that actually happened to you.  I'm just suggesting that therapy might help you past it..and therapists are non-judgemental, so it is something you can be honest and open about...and maybe finally begin to deal with on an emotional level.  

Whatever you decide, good luck.

If your girlfriend finds out she might beat you up and rape you with a large strap-on, if one is available.

That's the domme's job. Maybe you could even do a role play that punishes you for cheating. Maybe that would help you to accept it, or not.

The good aspects of your sessioning is that you are not falling in love (though you may feel emotionally attached), which would be pretty deadly for your primary relationship. And, you have an outlet for your sexuality, which would otherwise put a strain on your relationship (ie: you would start to resent your girlfriend and would always have your antennae up for a replacement.)

BTW: I am out to my wife as far as my orientation and she is ok with it, but not interested in exploring it with me. I am not out to her about sessioning as she would see that as cheating and would be profoundly unhappy about it.