i think it means.. they were having an affair, they used to have a lot of sex, and she was uninhibited, so that's why he says the line "i have my doubts you kiss your mother with that mouth." and then either they broke up, or just stopped having sex, and now they're being just friends. and he wanted her to break up with her boyfriend but "it's becoming more and more clear that your vampire boyfriend isn't going anywhere." - she has no intention of breaking up with her boyfriend.
i think it means.. they were having an affair, they used to have a lot of sex, and she was uninhibited, so that's why he says the line "i have my doubts you kiss your mother with that mouth." and then either they broke up, or just stopped having sex, and now they're being just friends. and he wanted her to break up with her boyfriend but "it's becoming more and more clear that your vampire boyfriend isn't going anywhere." - she has no intention of breaking up with her boyfriend.