I've noticed a trend and not just here at GFY but it my everyday life, too. It seems like all the 30something men dating or married to 18 year oldish girls always end up with their hearts broken after only a few years. Then it's melt down time and frankly it's annoying. I think I've come up with a temporary solution to help you all. First we must dig in to the root of this problem and try to understand it before I can give you any meaningful advice.
18 year old girls, much like 18 year old guys, know aboslutely nothing at all. Don't believe me? Talk to one. Oh, they'll tell you they have it all down, but for all intensive purposes they're still newborn children. All of their opinions and tastes are formed from a combination of their peer group and their family and they're just starting to think for themselves. Just a little.
The problem really comes in to play when they turn 19, 20ish. Because now they're actually starting to get their first clue about life. It's shortly after this they will question why a 30ish man is dating an 18 year old girl in the first place. Further, and more to the point, they will eventualy ask themselves why their boyfriend has no girl friends in or around his own age group.
Here's the solution guys: Check the age of consent for your state. In some cases it's as low as 15. A 15 year old really is no less intelligent than an 18 year old, and you'll get a good 4 or 5 years out of them before they clue in and leave you. After 4 or 5 years you should be able to reasonably convince yourself that you were tired of her anyway. Meltdown avoided.
Good luck and happy predatory behavior!