I like this boy. but its complicated. please help!!?

okay sophomore in high school. i have history with this guy "Paul". last year. and were really good friends and we have been since it ended. he now has a thing with this girl "Sandy" who he may or may not ask out soon. but were both like the flirt type so we always flirt no matter what. and weve been talking a lott more lately. and i like him again! im somewhat friends with the girl. what do you think i should do. back off or if i like him enough... idk i feel like a bad person all this. but you know when you like someone you cant stay away. we are honestly perfect for eachother too. not just saaying that soo many similar thoughts and looks on life and interests and everything. tips thanks