Should i act upon feelings that i have for my best friend who i get on with really well?

i have a female friend who i get on with really well, we text each other a lot and are there for each other to confide in. However, i wasnt sure if i had feelings for her a while ago, but i am now sure that i have them for her, what should i do? should i tell her and see what happens? or just leave it and hope they go away?