I'm not one to give advice on girls since I'm currently in a pretty complicated (and shitty) situation in that respect, but as far as losing weight goes I'm convinced it's possible for anyone.
When I was 19 I was 6'1", 285 lbs, now I'm 23 and 190 lbs. It's possible to lose huge amounts of weight, even after being overweight for most of your life.
For me it was just a matter of deciding I couldn't keep living like I had been living and making getting in shape my #1 priority in life (even over school, work, and friends). I built up from where running 10 minutes would leave me winded and aching to where I could run a solid 45 minutes and feel refreshed. I kept track of exactly what I ate and rarely drank anything but water. Over a long time the weight slowly came off. It was just really fucking hard and painful (especially at first).
For me anyway, just knowing that I could drive myself to stick with something that difficult gave me a lot of self confidence, and helped me deal with social situations a lot better (and it didn't hurt when girls starting telling me I was hot for the first time in my life).
Ok, I know there was a point to this
. I guess what I'm saying is that while confidence and personality go a long way, and I think it's definately possible to be overweight and happy, I think you shouldn't give up on getting in shape.
It's not just about being physically attractive to girls - it's about knowing you can do something that seemed impossible when you started.
Oh and on a side note I agree about ladder theory. I personally can't stand it (though I won't argue that it doesn't work). I tend to be far more attracted to girls that I like as friends than some random girl who hits on me at a bar.