I need to find out how to handle this.

I've been in a relationship with this wonderful woman (F37) for a while now, but she has a high-stress job that sometimes requires her to take time for herself. I totally understand the need for personal space—everyone needs time to recharge and reflect, right? However, she’s mentioned that in the past, her stress has led her to completely withdraw for days at a time, and that’s where I struggle. I know it’s not me causing her need for space, as she reassures me of that, but I can't help but wonder why I have to bear the brunt of her needing to isolate, especially if it’s due to stress from others. It’s tough for me to accept, and I worry that it makes me come off as unsupportive. I really question myself about this. Days without communication feel really painful. I’d appreciate any advice on how to cope during these times, and I’d like to hear your thoughts: Am I being selfish? Thank you!