Most Helpful Girl
Attraction issues are legitimate...especially when it comes to extremes (you said 'very large') or hard preferences (most people have one or two traits that they just aren't attracted to for some reason, while the rest are more of preferences of less or more degrees).
If he's attracted to her now, though...it's hard to guess if you will lose attraction to someone down the road or not. A size 0 girl could easily gain a bunch of weight, too.
I think females, for the most part, know that men's visual desires mostly trump personality. And in all honesty, while a man's looks don't make or break relationships for us to quite the same level, they do effect them. So trying to stay as fit and well groomed as you can opens more doors in the dating world.