Ok, i know I'm gonna get a lot of angry comments but here go's.
I think Finn was way harsh to PB.
1st. I don't think he ever "loved" PB. He's 14 and had a crush. You don't fall in love at 14.
2nd. She never flatout rejected him. The closest thing to a rejection was when he asked her if she "[wanted] to hung some more" and she said "that was like 5 years ago, you gotta move on, silly boy". She left him with a playfull comment hinting she still liked him.
3rd. The time where Finn put his head on her lap and she said "stop being weird". That is kinda a weird thing to do. That was not Finn saying how much he liked her and her rejecting him like he played it out to be.
4th. The only time he really tried to talk to her about it was when she was possesed by the Lich so that doesnt count
Finn needs to stop acting like a middle school girl with his love life.
Dont get me wrong, I LOVE FINN, but lately his been kinda weird.