So here's the thing. I (26F)  been on meds and going to therapy for almost a year now, and I feel like I'm starting to have more control over my emotions and myself. I haven't had a FP since I broke up with my last bf (27M) last November. Since then it's been nothing but pining and secretly hoping he'd come back to me.
So I recently found out he has a new gf and it was like a switch flipped and suddenly I just have no interest in him anymore, and I was like great, maybe I'm getting over the need to have an FP. 
So here's the part where I have no idea what to do. I've known my best friend (25M) since we were in highschool. Our relationship has always kind of been up and down, getting close and drifting apart etc. We're closer now than we've ever been and I've been starting to get the creeping sense of desperation for his attention to always be on me. I know that this isn't healthy thinking and I really don't want to get out of control and ruin our friendship. So my question is do I tell him that he is my FP and explain what that means? Or do I just ignore it and hope I can work through it in therapy before anything bad happens? 
He used to date a girl with BPD so he's really understanding and knows a lot about it. And before anyone asks no, I don't think I have a crush on him. This feels similar to having friends be my FP when I was a kid.