<human>: We've been together since we were 18. Lately we've been talking about marriage a lot. I love her so much and I want to spend the rest of my life with her. There's not a doubt in my mind. 

Last night, she sat me down and told me that she's not sure if I'm the guy that she wants to spend the rest of her life with. We've both only ever been with each other. I love that. I love that she's the only girl I've been with and I'm the only guy she's been with. She said that she thinks she wants to see what else is out there. That was pretty much the entirety of the conversation. She didn't say that she wanted to break up or take a break. That was it. It hurt more than you can possibly imagine.

I'm so confused. I didn't sleep at all last night. I just laid there staring at the wall listening to her breathing. I'm at work right now and I'm terrified to go home. All I want to do is hold her and kiss her but I feel like that would be a bad idea. Do I remain distant? Do I pretend nothing's wrong? Seriously, what do I do? I can't lose her. I don't know what I'd do if I did.

Could you distill the essence of the text into 1-3 sentences?
<bot>: Girlfriend [F22] told me she's not sure she wants to spend her life with me [M23]. What do I do?