I (23/M) have been friends with my girlfriend (22/F) for about a year now, and have been together for about five months. For the most part everything is good, she's a very kind and loving person, and in most aspects I'm happy with the relationship. However, there are a few issues, the most prominent of which is the fact that we haven't had sex in the five months that we've been together (Or the month or two that we had been dating.) 

We've gotten close once towards the beginning of the relationship. Sparing the details, during foreplay she told a joke that we both laughed at for a while, and as the laughter died down she mentioned that it killed her mood, and we could pick up where we left off another time. So, we stopped. It was no big deal, sometimes you're just not in the mood. 

Afterwards though any time she started to flirt with me heavily and I would respond in kind, she would respond with something along the lines of 'Hard pass' or 'Down boy,' because 'she's just teasing.' Being rejected so frequently and exclusively is doing a number on my self esteem, and the constant teasing is leaving me pretty frustrated. Strangely, she's frequently mentioned how 'healthy' our sex life is to our mutual friends.

Now, I'm someone who has a high sex drive when I'm in a relationship, and I really need physical intimacy. A decent part of a relationship to me is the feeling of being wanted, and expressing your want for your partner.  I've tried talking to her about it a few times trying to figure out her reason for never wanting to get intimate in case it's something that we can work on, but she has yet to give me a reason beyond just 'not being in the mood.'

Considering everything else in the relationship is very good I feel like it would be extremely shallow of me to break up with her over sex. But, it's a serious source of stress in my life at the moment. With her either unsure of the problem, or unwilling to talk to me about what the problem is, I don't see it getting any better.

WIBTA?