I'm a big guy. I maxed out at 310 lbs, I'm down to 250 now which is mostly muscle and the remainder of my beer gut. However, when I maxed out I ended up dating a rather beautiful latin girl who ran daily, etc. She liked me because I did my own thing, I didn't care what other people thought, I said what was on my mind, and because she could cuddle with me, and not feel like she was cuddling with a shaved greyhound.
It comes down to this... women are attracted to what they're attracted to. Plus, there's nothing wrong with being over-weight so long as its appropriate. All it means is that if a nuclear war happens, I'll be able to survive long enough on my body fat to wait for the skinny Calvin Klein model wannabe folks to become menu items, hah.
You could also try being a bit more respectful to other people's body types. I weighed 300 for close to a year, and it wasn't because I had bad habits - quite the opposite. I was only eating one meal a day, which has all but destroyed my metabolism. So, I started forcing myself to eat 4-5 meals a day, and I've been dropping the weight. Some people can be overweight for a number of other reasons, including medication, infirmary, etc. The point is, your body is yours, you should be comfortable with it. No one asks you to be comfortable with theirs. So if you're not, keep it to yourself, because it just sounds rude and arrogant (and to be honest, a bit put-offish especially for people like me, who're just coming to these forums to try to get more into a sport they're taking joy in, despite being overweight).
So, while you were critiquing the guy, did you actually try having a conversation with him to ascertain why it is your neice likes him? Or were you too busy staring at the belly?