Hey there,
It's perfectly fine that you don't like hearing about his ex's, since it bothers you I would suggest that you have a conversation with him and let him know how it makes you feel. If it's important to you I'm sure he'll make an effort to stop.
It's not wrong to not want to sleep with many people in your lifetime, but I'd be careful the way you judge people for how many people they sleep with. Sleeping with many different people doesn't necessarily mean that sex doesn't mean anything to them and that the people they sleep with don't mean anything to them. I know people who are polyamorous, meaning they have more than one partner and they all know about each other, sex is sacred to most of them too and they consider it to be a part of their spirituality even, they just expresses it in a different way. I wouldn't call it sick, it's just a different preference is all. There are people who do just date around, too, and it doesn't mean much to them. But again, it's just what they want for their romantic/sexual life at the time and if everyone involved is okay with it and enjoys it it's fine.
I personally am with you on the not dating around though, even though I don't really care if others do it I consider my relationships to be special and I want to focus on one person and love them as much as possible. I don't like dating people without meaning it and I certainly wouldn't enjoy sleeping with someone and not meaning it.
I hope this helped in some way and I wish you the best of luck.
