My two cents: Sex is an incredibly intimate, and therefore often emotionally charged thing. If she's in a relationship that is ending all that pent up emotion would be hard to keep under wraps after drinks and all the intensity of sex. She would do herself a favour by either ending it or stopping sleeping with others, but that's up to her. The not cumming's not a big deal either, it may be that you are holding back because, emotionally, it is such a difficult situation. Or it might just be that you have sex after drinking. I can never cum after too many drinks. Or if you're using condoms it makes it harder to get off ,or if you wank a lot, and are rough with yourself you can lose a bit of sensitivity for a while. Lots of reasons why it might be happening, probably not a big deal. Hope that was helpful.