I think I’ve developed feelings for one of my closest friends after she came to visit me — do I tell her or leave it alone?

I feel like I need completely unbiased opinions because everyone I know is too close to the situation. Some details/timelines changed slightly for privacy.

I met this girl through a mutual friend about four months ago, which sounds mental to me because it feels like we’ve known each other for years.

We became really close very quickly. Everything with her is just incredibly easy. We’re constantly laughing and taking the piss out of each other. We’ll make plans to go out and regularly end up just staying at mine drinking, dancing around, talking absolute shite for hours and somehow having a better time than if we'd actually gone anywhere. We nearly always end up one-on-one even when that wasn't necessarily the original plan.

For context, she also came out of a long-term relationship around the start of this year.

A couple of months ago I moved abroad. I've been questioning the move a bit and missing home, and recently she came over and stayed with me for a week. We shared my bed while she was here, but nothing sexual happened.

The week was just ridiculously easy. Having her there actually made this new place feel like home for the first time.

Then she left.

I genuinely wasn't expecting my reaction. I got sad saying goodbye, and when I came back to my apartment afterwards the place felt incredibly quiet. I woke up the next morning feeling a bit better but basically had the realisation of: fuck, I think I actually want this girl.

There have also been little things I'm now obviously overanalysing.

We've had joking conversations where I've mentioned hypothetically marrying someone else in the future and she's immediately inserted herself into the conversation instead. We've talked about other close friends potentially ending up together, and she regularly comments on how much fun the two of us always have.

There was also a situation where someone close to her basically warned me that i should never try get with her because it could ruin the friendship. When I told her about that conversation afterwards, she seemed genuinely shocked that they'd said it.

None of these things individually mean anything, and I'm very aware that now I have feelings I'm probably looking back at completely innocent interactions and seeing "signs."

The thing that's thrown me even more is our mutual friend. I finally told her how I was feeling, expecting her to be surprised, and her reaction was basically, "OMG obviously you two." She introduced us and knows both of us extremely well, so the fact that the idea apparently wasn't remotely surprising to her made me question things even more..

We currently live in different countries, although I'm going home for a decent amount of time soon and will obviously see her while I'm there. There's also a possibility we'll end up living in the same city in the future.

Part of me thinks I should just leave everything alone, get on with my life and see whether these feelings are still there after some time. Another part of me is worried that if I keep treating this as completely platonic when I know I want more, I'll eventually make things weirder anyway.

I'm not planning some massive declaration of love or drunkenly making a move on her. If I ever said anything, I'd want it to be something very low pressure, like asking whether she'd ever consider going on an actual date with me.

So, people who have been in this situation: would you say something eventually, or would you protect a really good friendship and leave it alone?

And from what I've described, does it sound like there could be something on her side too, or am I doing Olympic-level mental gymnastics because I've caught feelings?