As you can see, many of the people here have been in your husband's shoes and have been pretty hurt when their spouse had an affair, so there aren't too many of us who were the disloyal spouses. But I would be happy to try to answer your questions. First things first, I'm glad you've ended the affair. I realize it was hard to do and you may miss him, but you did the right thing obviously for many reasons. I'm also glad to hear you are working on your marriage. My suggestion would be that if there are things missing in your relationship with your husband, that the two of you work on those things, rather than turning to others outside the marriage. Okay?
On to your questions! You asked:
... This happened 3 times, and he would always contact me after a few weeks and start everything all over. More promises. More involvement. Then he would back out.
Actually there is a good reason for this. In some physiological ways, an affair can be very "addicting." When you two first meet and you first have a little crush, there is a brain chemical called phenylethylamine that is like a natural amphetamine. That's what makes people in love have butterflies in their stomach, a racing heart, sweaty palms, and that warm wonderful feeling. Here's a little article on The Chemistry of Love
. The chemicals are a natural "upper" so the truth of the matter is that if you like that feeling, you do sort of get addicted to it and want to get it again! I call that the "love-zing" and we all know what that is..that little thrill of being together.
So my guess is that he might call off the affair when he's thinking it's wrong (or whatever) and then miss that "love-zing" and the feeling of being interesting or wanted...and then after a little time be tempted to contact you again. In order to really end an affair, a person REALLY has to fight temptation to contact and has to sort of go through "withdrawal" because there is no more love chemistry. As you may guess, "withdrawal" is hard and at least for me, I did better when I replaced the temptation with something else--a new activity or new thought. For example, every time I had a temptation or missed the other person, I thought right then of something good about my spouse or went to hug him, to replace the "withdrawal" kind of thought with a "recovery" kind of thought. Make sense?
...My question is... if this was all about sex for him, wouldn't he have kept the sex going?? ... Was I used? Or is he feeling guilty once again?
Again I'm only guessing, but I doubt is was "only about sex for him." I mean I bet there was some element of that there, but usually it's much more about having basic human needs met. I'll give an example. Often affairs start maybe at work. You spend a lot of time with that person, 8-10 hours a day, doing similar things or at least understanding what the other one goes through. Generally, when you go to work, you dress well, look presentable, etc. And at work, you might compliment him on a job well done, or admire him when he deals with a really hard customer...and at home his wife doesn't really dress up much anymore and when she talks to him its to nag about money. Naturally, he starts to kind of LIKE you and flirts a little. You then feel complimented that he'd flirt so you feel pretty and wear a new perfume and flirt back... so ba da bing, it starts. And really what's happening is that you feel wanted, needed, smart, pretty, and interesting...and he feels wanted, needed, smart, handsome and admired. See how that's more emotions than just "sex"? If it was just "sex" you can buy that for $25 or get a lap dance.
Were you used? I would say yes. Was it heartless "using you and tossing you away"? Probably not deliberately, but here's the problem. In real life, both of you made a promise to your spouse, to "act in a way so that affection and loyalty are committed and dedicated to a private person to whom loyalty is due." That's what getting married IS. So the fact that he made that promise to someone else and then gave his affection and loyalty to someone else (you) so that he could get his needs met is actually in fact using you...maybe not maliciously but it is. Likewise you used him to meet some of your needs probably for a little attention, romance, compliments, taking the time to talk to you...that kind of thing.
So I hope that answers your questions. If you need any other help recovering your marriage or how to talk to your husband about it, just let me know!