I really wonder if, on a certain level, Tai isn't as wild as she likes to make out. She puts up this front of being this uber-sexual and incredibly self-confident woman but, sometimes, her reactions to Dora's emotional needs suggest that she's never really been emotionally intimate with anyone before. If anything, she's just as vulnerable as most of the other QC primary character girls.
To be fair, this is pretty much me. When it comes to sexual encounters, I am boldly confident. As long as it is just fun and casual, nothing really phases me and I will go into the situation without any hesitation or crises of confidence. However, when it comes to actual relationships, I am a complete mess. When I develop real deep feelings for someone, I am constantly second guessing myself, over-thinking everything, and just generally freaking out. I've identified with Tai pretty much from the beginning. When it was revealed just how UNconfident she is when it comes to actual romantic relationships, it just increased that identification.
I've only had two really serious relationships: the first developed out of a friendship with my childhood best friend; I ended up marrying her. After she died, it was years before I was able to let myself be vulnerable enough to fall for someone again; I am currently with that woman, now. Sex is easy, love is hard. When it's just sex and fun, you aren't really risking anything by giving it a chance, even if you get shot down. You didn't really invest anything, so nothing is lost. When you put your heart into it, you are taking a huge risk. Rejection of your sexual advances is nowhere near as devastating as rejection of your love.
Add in the fact that I never had much in the way of love shown to me growing up, my almost crippling fear of abandonment which manifests in an equally crippling fear of commitment, and you have a recipe for intense anxiety when it comes to serious romantic relationships that just isn't there with casual flings.