<human>: We've been together for about 1/2 year. She has a rare heart condition, arrhythmia, which prevents her from exercising too hard despite being on a track team. So I try not to put any more stress on her, but this mysterious problem is.

Recently, I [21/M] noticed something has been troubling my girlfriend alot and it has been affecting her usual lifestyle. She keeps telling me that everything's okay, which obviously isn't. For instance, she isn't sleeping well and has developed faint dark circles under her eyes. Although still the most gorgeous girl in my life :) I already told her I'm willing to listen if there are any problems, but I didn't press the issue.

Yesterday, I went to her apartment to check up on her, and seen that she was clearly crying before I got there. I had to ask, I just had to confront her about it.

Here's what happened when I tried:

Me: "Listen, I know that you've kind of had a rough time lately. And I want to help you out, but I can't do anything if you won't talk to me about it."

Her: "Sweetheart I told you, I'm fine."

Me: "No you aren't. It's obvious something's been eating at you. You can tell me."

Her: "Why is me saying 'I'm fine' not good enough? You're concerned, I get that. That's cool. But I'm fine, and it's nothing that you need to worry about."

That reply caught me off guard and I didn't know what to say. I feel like it's the boyfriend's responsibility to know the well-being of his girlfriend. What you guys think I should've said after that without coming off as a controlling boyfriend who wants her to spill out every secret? She's the first person I've truly cared about on a deeper level. It's been hard to do so.

Can you condense the text into three sentences or less?
<bot>: girlfriend not talking about her problems with me.  Always reassures me that's it's okay, despite being not the case.