Ick!  I don't know which way to go with this one.  On the one hand, I could take the position that "it doesn't matter where you get your appetite as long as you go home for dinner" and just leave it at that...It's pretty self-explanatory.  On the other hand, its really not that easy.

At least he is not lusting after a librarian

First of all, I don't want to know that my boyfriend, who is supposed to love everything about me, is out ogling chicks at the gym I despise the thought of him closing his eyes

But I'll bet your boyfriend does lust

while we make love and thinking that he might be imagining that I am somebody else.

If my boyfriend is checking out other women, he can have them, but he can't have me!

  .

I would feel terrible

And no woman wants to feel like you have chosen them for their stability but secretly desire a wild woman that offers little more than a bite of your sexual fantasy.

On the other hand, we are sexual

But that's the problem

beings.  Of course you're going to look at a beautiful woman as she passes you by.  The most important thing you can do here is let the woman that you are with know that she is the one, that you love her, and that nothing is going to interfere with that, and you have to believe it yourself.  It's really easy to fall into a spell where you believe that everybody else has what you want except for the person you're with. Learn to control your "lust" or you're really not ready for a mature adult relationship.

If none of this advice works for you, try this.  Look at these girls that you so desire, and picture them in the morning without their make-up; imagine them on the toilet; imagine them bitching at you when they are PMSing, because the truth is, if you're relationship has endured these things, you are lucky, and some chick in a thong isn't going to give you any more than you've already got.  If the woman you call your "soulmate" is really that, then you will be the sorry one if you step out of line.