Well yeah it's not really an obligation. It's more like just... a weird thing. Like if you're going over but have no intention of doing anything then you should be going in feeling comfortable saying 'no'. Otherwise... why are you putting yourself in that position? Which makes me think this guys situation is fine. Even though it definitely sounds weird.

Dude, wtf? Yeah, sometimes she says yes initially, but if you say something weird/creepy on the way, she might change her mind. Or if she comes over and all your decorations are Ninja Turtles, maybe she realizes you're not her type because she's more into Spongebob or something.

The thing is, if she is still into you by the time you get home, and you start making out, and you try to initiate sex, and she says no, the absolute best best best thing you can do is say, "OK, can I walk you home?" Make sure there's a next time if she's at all interested, and then you leave the door open so that maybe you will have sex, maybe lots of it, later on.

"Wanna watch me masturbate instead?" basically closes the door on any future prospect. Now you're just being a selfish asshole. And what are you as a man getting out of it anyway? Walk her home, then jerk off when you get home. She can't stop you from thinking about her when you do it. It's a win/win for everybody!

Plus, you've been a gentleman, and if it never works out, so be it because you're still going to come out ahead. Remain her friend because, if she's hot, she probably has hot friends and if you're not her type, she might hook you up with some other friend later on. She at least might think of you to invite you out places (or you invite her and her friends) and you've widened your social circle to include other girls who might like you more than she does.

Staying on good terms with the ladies always leads to better outcomes. Taking your dick out when she just said no to sex is the fastest way to Nowheresville.