Piper, first of all, you are not dirt. You made a mistake, or maybe it was a level higher up on the totem pole than mistake. Maybe it was premeditated but whatever the case, you did it and now you are sorry. One of the first things you need to do is forgive yourself and then forgive your H if he can't just follow in kind.
I don't think this is avoidable (me continually comparing you to my W) nor do I think I should avoid it. As you rightfully said, I took the approach early on with you that since you seem like my W in some ways, and I may seem like your H in others, then maybe me sharing my point of view may help. Well, with that HUGE preface, I have this for you.
Advice to my W (you) #1633 (lol)...
W, please don't be "unavailable" for long periods of time. I don't really care WHAT the reason is, and if there is going to be a reason that you know about in advance, i.e. going somewhere there is going to be no signal, etc., please let me know. I know it's probably innocent but I can't tell you how it drives me crazy that every time I can't get ahold of you my mind goes straight back to "that" place where neither of us wants to be anymore. Sure, this is largly MY problem but I really would like you to help me with it. I feel caught. If I just brush it off and think "oh, it's probably nothing." then I feel like I am ignoring something that USED to be one of the biggest signals of SOMETHING (she admitted she just would not answer her cell when she was with him). If I ask you about it, you accuse me of being hung up on the affair and still suspecting you at every turn. You say I can't get past it and you just get pissed...
BTW, Piper, does this relate to you at all?
W, I just wish, one time when I ask you a question like "why didn't you answer your phone when I called" and you suspected I was feeling paranoid, you'd just come out and say "I'm sorry. I know how it may make you feel when that happens and I assure you I didn't mean for it to. I was xxx..."
MY point is, my W ALWAYS gets defensive when I ask/confront her on these things as if I have no right to be suspicious. Maybe I don't but really, what I am looking for more than confirmation that nothing is going on, is a certain understanding from her. I am looking for her to WANT me to believe that nothing is going on, and as much as you (I mean YOU piper) say you think he doesn't really want to be happy, I think my W (and maybe you) don't really WANT me to believe you are being honest (either that or she's not) because otherwise why not do these little, common sense things, like have your phone out of your purse so you can hear the thing ring between 11am-1pm, the PRIME OM time? Wouldn't that make sense, but to her, it seems like I am trying to control her or live in the past. To her, since there is nothing going on anymore, why do I have to be that way? It's like she resents the hell out of me for my feelings and that sucks.
Anyway Piper, that was confusing I'm sure. The bottom line here is that I think one of the things you could do to help H the most is NOT get defensive when he asks questions of you. Maybe do as some have suggested and that is to set aside a specific day and time frame where he is free to ask away, and you answer his questions (for some LBS it IS important they feel they have all the info), then he agrees to drop it until the next pre-determined time.
I know it feels like he's persecuting you, but I really think, like me, he's just trying to rid himself of the pain and paranoia and maybe looking to you for help, help you're uncertain about how to give.