>Girl i've been dating might be an actual angel >She's

clearly you aren't meant to be then.
Shes just the first woman to ever give you time of day and you're falling for the "settled for a fatty" meme because you have zero self confidence.

also
>Implying its impossible for her to lose weight
Its a longer shot yes, since it's not something you can tactfully bring up, but she might lose weight later on down the road.

If the topic of sex comes up, just tell her you don't think you can do it because, while you like her as a person, you're not sexually attracted to her.

My partner is fat and took my virginity. I convinced him to go to the gym weekly for his health's sake. He's already lost 15 pounds since then. Even though I like touching his fat body, I am still interested what it will be like when he's a "normal" weight.

Even if he didn't lose weight though, being in love is awesome and I am happy and content with who he is so I don't see why I would end something good just to experience other people who might just end up being a disappointment and not worth it.