First off, you contradict yourself when you say that this is the relationship of which you have dreamed, (unless of course your own fantasies entail a man who fantasizes about barely legal chicas).
He's Never Acted On His Fantasies
Obviously this disturbs you, you have talked to him about it and he tells you they are harmless fantasies, and he has a point. If he has never acted on them, and never has any designs toward acting on them, then they are just that, harmless fantasies.
What isn't harmless however is the illegal film you mentioned. I hope your boyfriend knows that if that film is legit in it's proclamation then he is committing a felony in
to do with it.
This of course having a domino effect on you when you get to explain to your friends, family, and co-workers why they saw your man on T.V. last night in handcuffs.
You've Broken His Trust
What also isn't harmless is what you have managed to do to your own relationship, without (it sounds like), even realizing it.
How Did You Find Out?
The burning question on everyone's mind right now has to be, how in the world did you find out?
I've said it before and I'll say it again, trust is what BINDS a relationship. Once you
violate that you are hard put to repair it.
Case in point, you are/were in very happy relationship with a man, best relationship ever in fact, and for some masochistic reason you decide to spy on him. Or whatever. You dig something up about him that has to be very personal, and let's face it, considering the subject matter, a bit "turn-your-face-pink-upon-mentioning".
You betray the trust he has in you and in doing so, destroy your own trust in him, consequently leading to the dissolution of his trust in you.
This Is A Result Of Low Self Esteem
This looks to be a direct result of your own faulty self esteem. You couldn't accept the fact that there was a great guy out there that loved you for you and actually wanted to be with a cow like yourself, (no insult intended here, only personifying), and you just had to find the catch, didn't you?
The truth is, sister, if there is someone in your relationship who isn't happy with your "ample" breasts, it's you. If it was him do you really think he would "enjoy" them?
Get Over It
My advice to you is to get over it. People, men and women alike, fantasize. They are sometimes, not always, extreme or far-fetched situations that would never in a million years happen, that's why they're called fantasies.
Wild cheerleader orgies only ever occur in Penthouse, and when those lounge lizards write in to tell all about them, guess what? They're lying.
Work on yourself. If you are not happy with your shape, go to a gym. Ask your man to go with you. Work very, VERY hard to get his trust back, and keep your nose out of his computer, and you should be fine.