How should I handle this?

I need some advice.

My boyfriend is having health issues. He wasn't the healthiest person to begin with and now his choices are taking a toll on his body. I'm trying to help him the best I can. Reminding him to eat better, exercise, etc. But I'm starting to feel like a nag and a mom. There's also only so much you can tell a person to do. They have to want to do it themselves.

So now I'm feeling less and less as a girlfriend and more of a mom or nurse. We also are hardly seeing each other and when we do it's all about his health and how he's feeling. His health is now affecting our relationship. I don't want to sound like an insensitive, selfish girlfriend. I want to support and help him as much as I can. But this is now taking a toll on me. Our relationship is about how he's feeling and doing. I'm not feeling like myself either because I don't feel like I'm in a shared relationship.

What should I do?

Updates
7 mo
Part of my frustration is also that I, myself am a relatively active person. I like to exercise, I try not to way horribly.
How should I handle this?
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