Hang in there and don't beat yourself up about wanting to go down that path w/ OM. We have probably all have been tempted to do so, and for many of us, it was the lack of availability during that most vulnerable of times that likely kept us on the right path rather than moral fortitude.
I know you are cutting back your contact w/ this person, but I'd really question continuing texting. In part, do you think your H is above doing a little snooping when he goes through one of the inevitable swings of mood or starts to get worried that your changes mean you won't be sitting on the shelf where he left you?
I also know that you've mentioned several times about being remote and feeling isolated. This turn of events really drives home that putting an extra effort to figure out healthy activities that bring you into contact with people is in order. It is hard. You may have to look and drive further afield, but you need to think in terms of activities you'd like to join in and let the friendships follow. Isolation increases the vulnerability. Being involved with groups spreads the emotional support around. Sure it increases the number of candidates for a dalliance, but it also dilutes the possible intensity of encounters w/ any one person and the presence of the group helps keep up just enough self-consciousness about being detected that it lowers the chances of acting.
Finally, it is also OK to enjoy it. You deserve it. You haven't been getting that affirmation. Unfortunately, as other's have pointed out it is addicting. It also doesn't ultimately help you grow into a person capable of having healthy relationships. Instead of hanging in there and building the capacity to comfort ourselves, to affirm ourselves, to individuate, etc. we turn to a crutch that inhibits this necessary growth. That won't help building a new M with your H should he come around and you still want to do so, or have Rs in the future that don't repeat the same mistakes and dynamics that contributed to the trouble your M is in right now.
Besides, as an therapist worth their salt would tell you: you cannot have a healthy intimate (& I'm not talking about sex, but the kind of vulnerable sharing and mutually nurturing) R with anyone right now. Not your H. Not anyone.
As you have noticed, you really didn't understand how hard we were warning you that this was going to all be, but you are getting it. We wish we could spare you of that. You are way ahead of where most of us were during this phase, and you will have the support and feedback to try to at least make this painful time count for something good.
Good luck. Keep letting us know what is going on w/ your sitch and your thoughts.
Me: 50 W:43 S6, S3 M: 12 yrs. T: 17 M is bad & Not happy Bomb Mar '14 S 5 Feb '15 D Bomb 13 Apr '15 (but "no hurry") DB Coach May '15 Wants proceed on D Aug '15 Starting 1-on-1 negotiations Sept '15