Teasing can be hard. I eventually learned to see myself in such a way that the teasing did not hurt and I could understand why I was "teaseable" and either work on that behavior or tease myself when it happened. Being able to truly laugh at yourself and your foibles, to enjoy yourself in all your aspects is very freeing.

People I don't care about who tease me (mean people) don't bother me anymore because I don't care about them; it's like random strangers who don't know me making comments. I know me and know what I am doing, what my problems are, what I'm working on and how well I'm doing and can dismiss those who are ignorant and unkind without much thought; they're not part of my life and I don't let them in.

With Billy, I would try going over closer to him and the girl and listening/joining in their conversation, maybe getting to know the girl more, engage them to get a sense of if Billy really is ignoring you or doesn't "see" you because she is engaging him more. If you just observe a lot, I'd get in there and participate some or you will be more ignored because if other people are talking/teasing/being together, they're not going to notice the rest of the world so much. Get out of your head some and practice conversing with the others and see if you are noticed more other times. People "expect" certain things and if you get in the habit of being quiet, that's what they will expect and not realize it is not the way you want to be.