Friend’s girlfriend flirted with me...

My best friend’s girlfriend recently flirted with me at a party after getting drunk. I didn’t say anything to my friend about it at the time because I knew she didn’t mean it, even though she didn’t remember anything the next day. I have been getting some strange messages from her on Facebook though, and am starting to feel as if she is trying to get closer to me which makes me feel awkward. If I tell my friend this, he will confront her and she may just deny it, which will only cause unnecessary tension between him and me. I don’t know what to do because I don’t want my friendship to be affected in any way. Should I tell him what happened and let them figure this out, or should I just speak to her and try to understand what she’s trying to do?
If this is your best friend, you shouldn’t have a problem being honest about how you feel, especially if you believe it may lead to unnecessary issues down the line. If you have a problem with his girlfriend, and want to avoid any misunderstanding, it may also help to have a chat with her and get it out of the way. Chances are this is just being misinterpreted in some way and can only be addressed by you being direct and getting ahead of the situation.

Should I tell my girlfriend that I don’t want to consider a long-term relationship with her because I am not looking for something serious? I don’t want to hurt her feelings and feel as if she is more into this than I am, which makes me feel guilty.
If you aren’t looking for something serious, you owe her the truth because not telling her how you feel will only end up hurting her more. Relationships depend upon honesty, and the two of you being clear about what you both expect from this. The sooner you have that conversation, the better it will be for you both.