Which boundaries should I (Late 20s F) set with my online best friend (Late 20s M) after a confession?

r/

I (Late 20s F) had experienced two long distance relationships (LRD), each lasting for three years. They always ended because they no longer wanted to move to my area because they didn’t want to leave family behind. I completely understand this, and the thought is heartbreaking so I swore to myself I will NEVER get into another LDR again.

With that said, my male best friend (late 20s) of 5ish years confessed his feelings for me, which is somewhat mutual, as I am really close to him. Unfortunately due to circumstances, I do not want to do LDR and do not want him moving here as I would feel too guilty taking him away from his family and friends. I wouldn’t want to leave my family either. We both are in a huge circle of friends (mostly men) and I don’t want that to get weird ethier. I just want things to go back to the way it was but I know that won’t happen.

What boundaries should I set to keep things platonic without being mean?

TLDR: Best LD friend (M) confessed and feelings mutal but don’t want a relationship due to guilt and a promise I made to myself. What boundaries should I set for platonic only?