I had a very similar experience, we're still together years later and I still train. She's completely over it and no longer cares. The problem is with your relationship, it's got nothing to do with grappling, and this is just a symptom. But you have more options than you think. Keep in mind your girlfriend might have an undiagnozed anxiety disorder or something along those lines.

I'm not a therapist, but here are some ideas:

Ask her why it upsets her. She might not say it outright but the most likely root cause is that she's afraid you're going to leave her for somebody else. Point out that it's your favourite activity, that it keeps you healthy and sober, that you think it makes you a better person, and that it is going to deeply upset you to quit. Point out that she is asking you to do something that will make you miserable in order to stay with her. Tell her that it upsets you that she can't trust you. You basically have to make her realize that she is intentionally making you miserable, but you have to do it without making it sound like you're attacking her, or at least as little as possible. If this kind of talk goes well, consider a trade: You'll stop training for three months if she sees a therapist for three months about her trust issues. Something like that. If it goes badly, try a gentle breakup. Tell her you want to be with her more than anything but she needs to reciprocate, and she clearly doesn't consider your happiness at all. She might realize she's made a mistake, sort her shit out and come back to you.

It might also be that she's insecure that you find other activities more fun than spending time with her. If this is the case, you might just need to set aside more of your free time to be with her. Set a specific date night each week, or maybe even divide it so you have three nights of training and three nights with her each week.