Say you do hook with someone that has a lovely body will you leave them if/when she has your children? What if she has an accident and is disfigured and can't exercise and puts on weight? These may be things to consider as someone's weight (particularly a womans) does fluctuate throughout her life. FYI my BF had a similar problem when he met me. His relationships previous were mostly based on physical attraction but when he met me he felt attraction on many levels, unfortunately physical was right down the bottom. He is not a big person so I guess he felt a bit intimidated that I could fit into his shorts and beat him in an arm wrestle. His problems also crossed over into the bedroom where he struggled to perform as he was so used to seeing "perfect" bodies (not just in RL but through porn, media, etc). This wasn't the only reason but it contributed. Anyway I eventually said enough is enough and left but we have since reconciled and in the time we were apart he sought therapy for his various issues, a lot relating to his past, and each day we are working at forming a true connection. He never claimed to not find me attractive, he just struggled with my body not being a size 6 to what he was used to and thought he was most attracted to.
Have you met this girl in RL? I agree with Merry if you have met her and feel like you do want to have sex with her I think you will be able to get past it. It may just take some readjusting of your thoughts and mind processes. Also maybe evaluate your views on sex. If you view women as ojbects just to have sex with then this will have a bigger bearing on your situation than if you view sex as just another way of showing your partner love and forming an intimate connection with them. After all you like this girl coz it is her, not someone else.
Some people are drains and some are radiators... Keep clear of the drains and hug the radiators!