My boyfriend thinks that I shouldn't work my abs too much, because it will make them stick out instead of being flat. Any opinions on this?

Your boyfriend is wrong. He is probably talking about the way bodybuilders look when they take steroids for awhile and their organs begin to push their abdominals out.

You don't want to work them too much anyway because then they won't grow. The more muscle you have in that area, the more fat they are burning at rest.

IMO, lifting abs 2 days a week is plenty. I would also use weight-bearing exercises as well. If you are the type of person who does a ton of different types of crunches, ask yourself this: If I work biceps, do I stand in fron of the mirror with no weight and curl just my arms for 30 reps? Nope. So don't treat your abs any different than you do other muscle groups. Use weight-bearing exercises around the 10 rep range 2 days a week. You will be surprised at what that can do.

Hope that helps

Sporto

Sporto is exactly right, I train my abs 2 times a week and use weight resistance where at the most I can get are 12 reps...