Mixed feelings about my girlfriend

So I'll try and keep this as short as possible, but basically when we started going out (just over 18 months ago,) everything was great and we understood each other and I literally thought I was the luckiest man in the world. Over about the past 2 or so months, my feelings are starting to change slightly.
For example, I don't drink alcohol and never have and I told her that when we first started going out...and she was fine with it however now that she has started to drink more, she has started to say how she finds it weird and all this kind of stuff and she's worried about our future as we apparently can't go out to the pub and all this kind of stuff.

Another issue is our sexual compatibility. We have spoke about this about 3 times over the 18 months as I have a higher sex drive than her. The thing which frustrates me isn't the fact of her not having a high sex drive, but not willing to please me nor allow me to try and kiss her/arouse her in order to help her get in the mood. It just seems illogical to myself and I don't quite understand it.

Also, she has not long gone on holiday with her family. I've found this quite hard as I've always been brought up in an open family in which any partner of ours is classed as family therefore they go out for meals with us and holidays sometimes whereas with her family, I have been out for one meal and my girlfriend wouldn't even ask about me joining them on holiday because according to her, all hell would break loose. So despite her family being welcoming in the house, other than that I am pretty much classed as 'the bit on the side'.
Following this, whilst she has been on holiday she has told me she has been hit on twice by other lads. I appreciate her for telling me the truth however I was kind of shocked when I heard it initially as I would have thought that if anybody had have got so close to be able to move in she would have said something. Apparently one of them kissed her just above the lips and so although it's a not a major catastrophe, I'm still not overly happy as it's not nice to hear that your girlfriend has kissed somebody else.
She also hasn't really been contacting me whilst she's been away and whenever she does contact me, it is after she has had cocktails and it is early hours of the morning not to mention she is generally talking to me in a selfish mannerism as well as just in a rude way and it's really starting to get to me.

After some thought with these recent events, I am starting to get really quite down about it and I don't particularly want to break up with her but I (especially at the moment) am not happy and so finding it quite hard but I just don't know what to do given I feel as though I'll bend over backwards to do anything for her but when it's reversed it is very rare she'll go out of her way to do something for me generally.

Does anybody have any advice on what I could/should do? Thanks in advanced.

Family stuff is normal, family stuff varies hugely, so don't worry about that, my ex had a very very odd family dynamic which I found hard to adjust to

As for the drinking thing, I can totally relate, I hate clubbing and dancing, which girls say they are OK with when they meet me, but roll on 2 years or so and it becomes a massive issue

The sex problem is unlikely to change, as it is often linked to the point above, many girls will very slowly change how they feel towards you, even if they don't want to, and a sexual incompatibility is miserable for the one with higher sex drive- the girl just tends to get irritable and snappy , don't really understand how bad it makes the guy feel

Got to communicate, it can be awkward or difficult, but you got to explain how you feel, and if she doesn't listen then you have to seriously consider your options

If your girlfriend doesn't want sex, she doesn't want sex. You kissing her and trying to get her in the mood when she clearly isn't in the mood will go down like a lead balloon. You can't force arousal.