I'm not sure HOW to get rid of these nauseated thoughts, but if it makes you feel any better, I also felt somewhat the same with my ex. We went to the same school together, and I since the break up it was all awkward passing by around the hallways and avoidance, and during the millions of unsuccessful "trying to make up" sessions we always touched each other, like a handshake, or a hand holding, leaning on each others shoulders, nothing more. I often got nauseated thinking about it, I felt "contaminated" too, not just touching, but even BEING in the same class with him, BEING in the same school with him, and there was this room in school I always hung out myself alone to cry it out during my free periods, and when he started hanging out there, I literally felt like sanitizing the room and a part of me was taken away. Do you feel something similar?

Anyway, from my experience (from what I understand myself), what I have attributed to this "nausea" is what they call association. For example, the room in which I associate my crying, my "let it go" sessions, my emotions, a safe haven, and suddenly my ex hangs out in that room, it just somehow breaches an unspoken boundary. Whenever he touches me, it felt like "get off me, I don't want you here." It is the pain and grief of him being there that made me sick to the stomach, basically emotional pain (or trauma, whatever you'd like to call it) that he is not aware of, and yet hurts me without realising it. (the hurting = the nausea) The more he does what he does, the more sickened I feel. I have puked before because of this as well. I'm also clearing out his stuff.

How to stop it? Well, I don't have any surefire methods, BUT I DID stop. I basically deleted everything about him and cut off all contact. Perhaps only time can heal this feeling. That was my way of doing it, basically how you'd get over an ex. I'd be lying if I say I still don't think about him, and that it's like a broken bone that has healed, but sometimes the healed part throbs, and hurts.

Hope this has helped. I apologize if it wasn't and that I didn't seem to have fully understood what you meant.