You asked "Would you fuck, date, or marry a fat guy?"
I would. Without hesitation if they were good people.
The whole concept of beauty is subjective and what is considered mainstream beautiful is undeniably attractive but beauty is from within and mainstream beauty doesn't (or hasn't) included that very often in the past.
Right this very second, there's a guy overseas that I want to fall madly in bed with. I don't know him very well and he's a bigger guy with a nice rounded shape and he's nice.
If I could, I would sleep with him. I would want to try dating him but historically dating isn't my strong suit and the guy is definitely worth putting a ring on but I'm not the marrying type right now so I wouldn't marry him.
...but cold beer on a hot day, while fucking each other senseless in the raw and rugged forests of Ontario. That sounds like a fun time to me.