I know that Finn is like the world's biggest moron but with being a part of celebacy club and having a single mother you'd think he'd be all up on protected sex and not making an idiot "teenage dad" out of himself. *sigh*

But I think he'd also be willing to put up with whatever rules Quinn set for him, if he could just get into her pants. At the celibacy club meeting she was all like "Don't you dare say the C-word!" when Rachel mentioned contraception, so I think Finn would be trusting and gullible and count on Quinn to make sure nothing happened.