Marka said:
I think, that one issue that comes up in this aspect of relationships, is because the non-ABDL partner; my wind-up feeling that they are having to compete - with their partner's AB/DL interests... And, where the AB/DL partner may be particularly protective of these proclivities; an actual (inadvertent -or, not-) competition; may genuinely exist...
I think Marka really nails the core of the issue here. As someone's romantic partner, you, Stich, have a desire to be seen as the primary object of your partner's affections. Part of that, I think, is a completely fair and legitimate desire, and part of that may not be a little bit unfair and not so legitimate. You'll need to think about it and untangle it a bit. Let me explain what I mean, and hopefully this will be helpful.
I think in a relationship, there's an aspect where each person involved has some needs. Those can be physical, like wanting a certain amount of sex, or of touching, hugging, cuddling and similar. They can be emotional, like having someone to offer support when you're feeling bad, or a confidant for your troubles with the stresses of life. They can be mental, like having someone to debate with about your favorite movies and music. These needs are all totally legitimate, and if you feel like your boyfriend's focus on diapers means that he doesn't have the time to focus on you the way that you'd like, you should let him know and talk together to see if there are things that either or both of you can do to help make sure that your needs are being met. A relationship that's only you providing things to your boyfriend while not providing things that are fulfilling to you isn't a good one.
On the other hand, sometimes there is a sort of unfair jealousy that can creep up. We as people, sometimes worry that even if we're getting what we want right now, we might lose what have in the future. Ignore diapers for a moment, when thinking about this. Many, many people get upset if they see their partner being friends with another person of the opposite sex. Or they'll get upset if a partner is spending a lot of time on some other activity like work, sports, games, etc. Because we're people, and we get worried that the partner's focus on something else means that they're losing interest and we'll lose what we have. This sort of jealousy, however, is unfair. If your needs are being met, but you still feel upset because you don't want your boyfriend focusing on anything but you, that's not great and is unfair to the boyfriend.
So, think about your situation from both perspectives. How much of the problem is that your needs in the relationship aren't being met because he's focused on diapers, and how much of the problem is your fear that his focus on anything other than you means he's losing interest in you? I'm sure there's at least a little bit of each one there, so see what you can do to pull them apart. And then go talk to him, let him know you're feeling a bit worried about this, that maybe you're feeling like you need a little more attention from him, but that you also want to support his ABDL side, and see if you two can figure some things out together that will help improve the situation.
. Just make sure you're confortable too. 
