Hi everyone, I'm an 18 year old guy living in Australia, and I could really use some advice on my current situation. I've been seeing this girl, A., for a few months pretty irregularly (like once a week or so) but we keep in contact over Facebook constantly. I know she likes me, and I like her, but for whatever reason she doesn't really excite me (I don't just mean sexually), I just feel really comfortable around her. Don't get me wrong, she's attractive but I just don't feel much spark. Oh and I should mention, she's a friend of my sister so that's another reason I really don't want to hurt her.
Enter girl C., who's almost the complete opposite. She works at the same place as me, although we've only had a few shifts at the same time, and we've been to a couple of the same parties. I am absolutely obsessed with her - she's exciting and interesting and fun to be around (and sexy as hell, like that matters psssh). We're friends, but not that close due to rarely seeing each other; she's hinted a couple of times that she likes me more than that. Then a week or so ago she started going out with this other guy (so of course now I'm beating myself up for not asking her out ages ago).
Before she started seeing this guy, I thought I should just try to get to know C. better so I could tell if I just had a temporary fixation on her or whether I liked her enough to ask her out and stop seeing A. Of course I still want to do that, only now I feel like a complete dick. Even if I ignore C., I still can't stop thinking about her and that's making me really confused about A. who now seems boring (which sounds terrible) - and I'm a bit ashamed that I'm pretending to A. that I'm more into her than I currently am. At the same time, I don't want to stop seeing A., because she's my first real relationship, I do like her a lot as a friend and I don't want to lose that, and because I'm worried that I'll just get over my obsession with C. and realise that breaking up with A. was a massive mistake.
Sooo, what do I do? At the moment I'm just being dishonest to everyone and it's not going to make them (or me) happy :/ I'd really appreciate anyone's advice.