I (28m) met my neighbour (30f) during lockdown. We became best friends, but now things are a little messy

So i?ll try and keep this brief. Back in May during the lockdown, I met my neighbours for the first time. We?d have drinks every night over the wall separating our buildings (at a social distance of course). Its safe to say we became good friends in a very short space of time.
Fast forward a few months, I became very close with one neighbour in particular. We?d hang out day and night (neither of us were working), go for walks, joke around and tell each other everything. It was so nice to have this amazing friendship develop from such crazy and anxious times.
So one night I went round to hers to watch a movie and we ended up sleeping with each other. lt felt like a very natural progression of our relationship and honestly it was amazing. This happened a few times, until one night when I noticed that she was acting strange and a little distant. I knew something was up, but she wouldn?t tell me. I?d go to kiss her and she?d turn away.
Anyway a few days ago I found out that she started dating another guy and that they slept together. Obviously I?m confused and a little hurt, but its not like we were exclusive. I?ve talked to her about it, but shes not interested in having a relationship (with me at least). Perhaps she just wanted some intimacy, I don?t know. I feel like I?m in a difficult position now, as I just started to develop feelings for this person. I?m not sure I can go back to being friends, however I don?t want to throw away the friendship we made (also it doesn?t help that she?s literally next door). What?s the best approach here?
TL;dr Became best friends with my neighbour over lockdown. Things got messy after we slept together, and now I?m struggling to remain friends.
UPDATE: I just wanna say thanks for all the advice. It always helps to get the opinions of others and reading through peoples similar experiences. I feel like I have some direction now!


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