You can't avoid taking her places, that's not going to solve anything....if you got a hot gf, guys are going to check her out.....period. I actually kind of like the fact that guys check out my gf, there is something satisfying in it..... Anyway, the problem is is that his gf seems to like the fact that she's being hit on and might be overly flirty with these dudes. Thats a major red flag IMO.