She's a former university classmate of mine. We've known each other for like, 6 years. Last 3 of them we've been extremely close. Total openness, close skinship, mutual high-effort assistance. Sometimes we even stay at each other's houses for weeks. Quite a contrast to awkward (mostly because of her default emotional coldness to other people) interactions before.

Her bf (who is also my friend, to a much lesser extent, but this is a long-standing relationship) i studies in another city, keeping in touch with her mainly through calls and 2-3 real meetings a year. He's probably going to stay in this city because of career prospects, but he won't admit it completely because they have an agreement that he'll come back. I don't know much about his feelings because it's obviously uncomfortable for both of us to discuss it. He started studying 1.5 years ago, and will graduate in 0.5 years.

She is not satisfied with this situation, but she does not end the relationship due to problems with determination/anxiety. I'm not interfering because of the obvious conflict of interest. While they were dating, I had several short-term affairs, and I discussed them with her, mostly treating them like a coolstories.

2 days ago, unexpectedly for her, I returned from a two-month business trip that could have been much longer, and my first priority was to meet her, so yesterday I visited her at home. We were sitting in the kitchen, she was cooking a week in advance (she was too busy to do it on weekdays) while I was working on my laptop, having a slow conversation with her at the same time. Suddenly she stopped doing what she was doing and sat on my lap and hugged me tightly, whispering that she "missed me very much." We stayed like that for a few minutes. It was a moment of realization that I would rather die alone than be with anyone but her.

A year ago, she said she didn't know how to classify our relationship because of their extreme closeness. Then we came to the conclusion that the closest concept is "best friend" yet we had't . Right now I'm not really sure and literally have no idea what to do about it.

TLDR: I have a friend that is a little too close to me, which I have romantic feelings for, yet I probably can't say it to her.