ItsABoy,
Your thoughts and fears are not at all unique. I have shared many of them; you're not alone.
You've expressed your need both for intimacy with a woman and intimacy with diapers. I've found that I have both needs, myself, and they come and go, with each taking "center stage" at different times. When I'm totally into one, I often find myself with little desire for the other. Other times I want a bit of both, and it all depends on my mood and on what's going on in my life. It can be very hard, though, to reconcile the two, especially when there is enormous peer pressure and societal pressure from both sides saying we have to be exclusively one thing and identify with only one pleasure. (If you're heterosexual, you had best be masculine and find your only pleasure in women, if you're ABDL you always need to be diapered, if you're gay, you always have to play to society's "gay norms," etc.) The truth is that none of us ever really fits these molds.
So when you're with a woman, explore and enjoy your feelings with her. When you're in diapers, explore and enjoy those feelings, too. Your own sexual desires and pleasures will be unique: everyone's desires are different. Relax, have fun, and explore what really works for you, because the more you know about yourself, the more you can articulate to others. Also listen closely to what your partner has to say and respond appropriately.
The most important part of any relationship, whether it's with a woman, or even with yourself, is honesty. Let your girlfriend know early on what works for you and what doesn't. If your religion has guidelines about sex, follow them as best you can and be honest about them. Also be honest with yourself (and anyone whom you are dating seriously) about your diaper side. Don't try to deny it or make it into something it's not. If the person you're dating really cares about you, she will honor your need for diapers, even if she doesn't wish to participate, herself. She might tell you about her own unique sexual need, too. It's all about trust (in others and in yourself) and communication.
You're no weirder than me or a lot of folks on here! Hope this helps a bit.