Is it normal to feel sick about other people cheating?

First of all, sorry for the bad english, I'm from Brazil.
I'm not religious, or a saint, far from that, if I'm a single would try to sleep with different girls every week, but if in a relationship, I'm faithfull. It makes me feel so bad, even watch tv ou hearing stories about that, I watched a show called Cheaters on youtube, and it makes me feel so sick to the stomach. I kind know it's silly and dumb, but one time, in a episode of HOUSE on FOX, a father sleeped with the son's gf, I almost trow up!
It is just me? Am I crazy? Here in the site about this same subject, one guy comment something like that: "Get of your high horse, it is the 21st century."
This also bother me, this way of thinking that hurt someone else like that it's normal or acceptable.
The bigger problem is that affects me in relationships, I have a hard time trusting my significant other. I'm not like a jealous chick, calling or checking the other person messages, in my head, I use logic, put myself together and I see there no actual reason to be suspicious. But every time I see something like that, I imagine myself in that position and it just hurt's me.