I also suspect she is in fact using you. You said she had a kid 6 months ago? So I doubt she's hitting the club scene any time soon and there you are with the D on demand for her, at the end of the day, she knows her Mum will eventually forgive her esp. if she makes you out to be the predator should the secret come out. Best solution, tell your GF, move out and never see either of them again. If you're attractive enough to get some decent MILF action and her daughter, then you won't be single for very long.