Just my two cents about motivation.
Oscar is probably right, at least I've found that to be the case, you need to acknowledge the sexual attraction/energy and use it constructively. It doesn't mean you always act on your impulses or be an asshole about it, but if you don't admit that you're a horny hetro guy and the female model before you is sexy then I think the photos are usually stilted and fake looking.
What I find creepy is all the men who photograph hot and/or naked women and then claim that it is 100% platonic and just for "art and an appreciation of the female form" without considering the person they are photographing is any sort of individual -- those shots are usually cold and sterile, and when they try to be sexy they reek of creepiness (to me.)
Make portraits, not nudes, even if the model is naked.
I have a great wife. She understands and for me at least, hanging out and shooting with a cool young girl fulfills my needs for friendship and fun -- better these girls than some 50-yr drunken suburban golfing buddies, right? -- and my pictures get a lot of attention. It's simply a matter of choice, I rather go out and have beers with crazy 22-yr old Meagan than to hang out with men from my own age group and class. I'm only friends with smarter, interesting young women -- no bimbos -- and they're fascinating because that age is a time of struggle and change, blah, blah, blah and there is always some drama to talk about. I bet you would too if you thought you could do it, but most people are too uptight to do what they really want to do.
But yeah, I'll opening admit I'd bang them all senseless if I lived in Utopia and they were into it too. That I don't/won't/can't is just reality, but I still get the benefits of having a fun time and getting good pictures. And yeah, on the rare occasion that you "have a moment", it makes you feel like a million bucks. But I also get satisfaction in knowing that I've helped a lot of my friends with difficult decisions and probably been a good influence on them, at least in terms of having a reasonable adult to turn to. Some of these girls are from some pretty tough situations.
Be open about it, admit your motivation, define your intentions, and just be a decent guy about it. Your partner will trust you and you'll get better photos.