I'm fat as well and wear what I like - thankfully it just so happens I don't like to wear stuff that has my fat rolls hanging out though.
I'm just being honest here, as someone whom has struggled with my weight all my life, I don't understand people whom are overweight, and want to dress in ways which don't flatter their shape, and instead have it 'hanging out'.
If its entirely due to confidence and not giving a shit, that's genuinely what you want to wear - then fair play to you. You can absolutely wear whatever you want whether someone likes it or lumps it.
I wouldn't want to date an overweight man who insists on having his trousers sitting below his belly so his belly roll flaps over it, on show, though. Sorry - I just wouldn't. The overweight is fine, the belly rolls out, no. I personally feel its a lack of decorum and self awareness really, because it's obvious the clothes aren't fitting him properly/he's not wearing them properly. But then I wouldn't choose to date a man in the first place who dressed like that. Surely your partner must have known how you dressed when you started dating? Or has there been some change in either your weight, or your style, since you began dating?
He's not entitled to tell you what to wear. He's entitled to be honest if he doesn't like it though.