Do not.. under *any* circumstances, spend time alone with this woman. I also suggest you start finding other ways to occupy your time. Find a new hobby, looks for groups in your area that have similar interests to yours, ect. You are playing with fire and it will result in immolation. Don't do it.

Might want to confess to your wife.

Women come and go, unlikely to be worth losing a wife and a best friend over.

I don't know if you currently have a wife or girlfriend so it may just be loneliness talking. My advice: Take a sabbatical from the entire friendship. Go do something else for a while and find yourself. Coz all the fantasies in your head is not how it's going to turn out, trust me.

Feeling are natural and cannot be helped. If you don't cut any contact with her than yes, you are.

I would speak too professional. I don't think it's her you want. could be someone like her to give you whatever she's giving your best friend. She feels safe to confide in you. you shouldn't ruin that