Can’t finish from her

I (18M) and girlfriend (19M) have recently started having oral sex and I’m a little worried because she cant get me off. I’ve never been with anyone before her, so I have no idea what it should be like, but she has a lot of experience and says it hasn’t been hard for her to get off her previous boyfriends. Our nights are pretty much talk, cuddle, I get her off, she tries to get me off but after a while has to stop because we both know it won’t work, she starts apologizing to me and asks me if I’m gonna leave her, then I go down on her again to affirm that I won’t, and the night ends with her being incredibly insecure and saying that she’s ugly, isn’t skilled enough, and that I’m going to leave her. I genuinely enjoy doing things for her and getting her off, and I don’t mind if that’s the majority of what we do during sex, but at the same time I really want to be able to get off, and I don’t think our relationship will be able to survive if I don’t. Although I’ve gotten much better about it recently, I think it may be in part due to masturbating a lot all through high school. I do it about twice a week now, and am trying to cut it out entirely, but I’m kinda worried the effects are permanent.

Any tips?