When Finn Hudson spoke to Rachel, he didn't know what he was trying to do.
Okay, that's a lie.
He knew what he was trying to do- he just wanted to know why.
Why was her telling Rachel how much he didn't want to go to prom with Quinn? Why was he so upset that Rachel was going to prom with Jesse St. James? Why was Rachel going with Jesse? Did she not remember all her did to her.
Finn isn't perfect, and he may have broken Rachel's heart too. But he didn't egg her. Publicly. He didn't lead her on.. Did he? No, he couldn't have.
When Finn told her all about not wanting to go to prom with Quinn, he was wishing she'd tell him to not, to go with her instead. But Rachel is too nice, and what would Finn have done? Blamed Rachel later? Said she'd convinced him to cancel Quinn's arrangements?
No, Finn didn't quite know why he'd spoken to Rachel that way.