<human>: My fiancee today had a bit of a breakdown and at first kept saying I didn't really love her, I was just staying with her ( my first gf ) because I hadn't experienced anyone else. I told her this wasn't true, and I loved her and was happy with her. Then it turned into a "its always about you, you, you.." and how she always does so much for me as if I don't do anything for her, don't adequately show her affection and don't make her feel loved. I asked what I could do differently, what more she was needing / wanting and she couldn't answer. I do my best, and I know I'm busy with school and work, but it's certainly not a 1-sided relationship. Later on I lay down next to her and after a while she says she is afraid of only being with 1 person, and missing out on experiences. 

I feel like she is really wanting to break up with me, but I think she is afraid to. We've been together for 5 years now, and haven't had any big relationship problems. I don't know where this is all coming from. She did just take a 3 day trip to see a friend from high-school in a different state, but I trust her and don't think she cheated on me. Maybe I'm just ignorant and missed a lot of the signs, but I feel like this is all a really quick turn around on how I thought things were going. I'm really scared to bring up the topic with her, and we haven't spoken for about 5 hours now, I've only seen her when she walks past me to go to the restroom where she closes the door (which we never do. no idea what shes doing in there..) and stays inside for 10 minutes. Any advice /r/relationships ?

Can you condense the text into three sentences or less?
<bot>: Fiancee (together for 5 years) suddenly brings up her fear of missing out on experiences and only being with 1 person without any prior indication of relationship problems (in my opinion). How do I handle this conversation?