I'm sorry to hear that you're going through this. It's important to communicate your feelings honestly while being respectful. Here’s a message you can consider sending:
Hey [Her Name],
I hope you're doing well. I've been doing a lot of thinking lately about our relationship, and I feel it’s important to share my thoughts with you.
I’ve noticed that you've been distant for a while now, and I can't help but feel that I'm often waiting for responses that never come. It really hurts when I text you and see that you go offline without replying, sometimes for hours. I get that life gets busy, but it does feel one-sided when I’m waiting for a small response, and I can't help but feel like I'm the only one putting in the effort.
Relationships require both people to work together, and I just don't see that happening right now. I truly value the time we've spent together, but it’s become clear to me that we’re not on the same page.
I think it would be best for both of us if we stop seeing each other romantically. I really do care about you, and if you're open to it, I’d like to stay friends.
Take care of yourself.
Feel free to tweak it to make it sound more like your voice. Good luck!