Background: My ex and I broke up a few months ago after many years together. It was sudden and painful. After that, we had lunch once, and other than that, we exchanged keys, slept together once that night, and then just sent a text here and there, or had a call once a week or so.

He has since entered into what looks like a rebound relationship. It started two weeks after he dropped off my keys. After seeing a photo of them together, it's pretty obvious she's more into him than he is into her. The body language in the photo says it all. Last time he and I spoke, he admitted that he still had feelings for me, and loves me. But also, I got it out of him that he and his GF had only recently slept together. (I guess they waited a couple of weeks.)

I'm disappointed in him. When he began dating me he was a good 7 months out of a 2.5-year relationship, and whole. This rebound started only 2.5 months after nearly 7 years with me. I did tell him (for the sisterhood) that it's actually a pretty lousy thing to start up with someone new and have sex with them while you still have feelings for someone else. Someone did that to me once a long time ago, and I remember how it felt, and I couldn't do that to someone else now. It's basically using the new person to hide from your own pain. She knows he is fresh out of a long relationship, and she chooses to get involved, so if she gets hurt, it's her fault as much as his, and, yes, that's their own mess that they are creating and none of my business. Only reason I pressed him to know is because I was wondering if he had slept with her before he dropped off my keys and if I needed to go get tested. Also, if they are sleeping together, in his way of doing things, that makes them BF/GF, and I would know there would be no way we'd get back together.

Issue: My issue is that I am, quite literally, physically nauseated by the mere thought of him. But here is the catch: I'm not sickened by the thought of him with her. A lot of people torture themselves with images of their exes with the new person, and go a little bit off the deep end like Tom Cruise in Eyes Wide Shut.

This isn't that. I'm sickened by my memories of what I did with him. Once he said he slept with her, it was like flipping a switch. It was like he became contaminated to me. I used to greatly enjoy sex with him. I loved his body, loved touching him, loved our chemistry, knew every inch of his skin and topography. And now? Any thought of touching him, kissing him, looking at his body, or doing anything with him gives me that drooling feeling you get right before you puke, and I have to get up and drink some Diet Dr. Pepper to settle my stomach.

I've never experienced this before. I've fallen out of love with people, lost my attraction to people, and lost interest in having sex with them, but I've never left a relationship feeling grossed out. Heck, when my ex-husband met someone, I was happy for him! I've never gone from finding someone attractive to being repulsed by him in such a complete 180. Maybe it's because I lost so much respect for him with the way he is using this girl that my physical feelings for him mirror my emotional ones?

I know the pat answer is "just don't think of him," but that's not exactly practical or realistic when I'm doing things like clearing out his old messages, getting rid of things he has given me, or just out and about and see something that reminds me of him.

Has anyone ever been through something like that? If so, how did you stop it?

As much as I don't mind dropping a few pounds (I'm trying to lose 15), I'd rather do it a better way!

Thanks for any gentle, nonjudgmental insights you can provide. This is really befuddling to me.