Have you talked to him about how it makes you feel when he discusses his sexual relationships with ex-girlfriends? It is obviously bothering you and making you feel bad. If you tell him that it bothers you and he continues doing it, he is being disrespectful to you. IMO, it's also disrespectful to those former girlfriends. Personally, I like it when a guy shows more respect than that for women in general. Have you had a frank discussion with him about how you're feeling about all of this?