Posting my second time ever to give my two cents. I am about OP's age, and have a very rough road with how I approach this. As I've gotten older I've also gotten bolder, openly telling girls who I like that I like them for who they are, and their bodies are a turn on as well.
Recently, however, I got into a discussion with a girl about feederism and fetishes, and she at first said she would try it, but later decided she didn't feel comfortable with it. That's fine, I said, no biggie. I don't need you to feel uncomfortable just trying to make me happy, I'm happy with just you as you are. All of this would be well and good, except she told a mutual friend of ours, who in turn told another friend, and when I met up with them at a party a few weeks later the two friends asked me point blank if I like fatter women, seeing as I had been with one of the friends in high school and she was a bigger girl, and she knew a few other large women I had been with.
Flustered by the surprise questions about my sex life, I did what any idiot would do: I lied. I told them that I knew this girl had a crush on me, and that she had a fat acceptance post on her tumblr page(it's a really wonderful post in all honesty), and that I just wanted to know how far she would go with it. I ended up cutting ties with this girl because I was so afraid of what people would think, and I look back on that moment as a peak of my cowardice, considering I have no problem admitting I had gay sex with my best friend freshman year of high school multiple times.
Now I am just getting into a relationship with a new girl, and have vowed to be honest with anyone who asks me about it, because if they don't like it, fuck em. I am still timid about going on dates with her, but I am going because why should I deny myself happiness because of strangers.
In conclusion, OP, I strongly suggest you push yourself out of your comfort zone. Don't make some big Facebook announcement or anything, just tell your closest friends when you get a chance and be honest if anyone else asks. That's all. My roommate has a thing for Asian women, even though his parents are wary of it, and you know what he does? He dates Asian women. You like fat girls, and have a girl you clearly are interested in. Date her, and worry about what she thinks and nobody else in this matter. I hope you get the girl!