Do boys only want is sex in relationships ?

It depends on the guy. Some do. It's something that most guys think about. If they are younger or more immature, they are more likely to only be interested in sex. I always heard the general rule was that people don't appreciate or value that which comes too easily to them, and that goes for guys and sex as well.

Who goes through the work of keeping up a relationship just to have sex a few times, when they could have had sex without putting that much time, energy, and feelings into something?

Depends I'm into sex relationship because I love sex not all guys are like that it's just some guys or 50/50

No, eventually people want sex of some kind, unless they are asexual, or have some sort of hormonal imbalance. You don't have to give it out if you don't want to, but of course you face the consequences of that decision. Maybe that guy wants to live his life having sex 5 times a day, then if he's proactive he'll go get that, or maybe he really loves you and will respect your decision and be with you anyway.

Most of the times.

based on my readings, no. Things like friendship and affection are probably more important. But my reading is based on pedophilia. So maybe outside pedophiles, people only care about sex. o.o

No .. they'll want you to cook them a nice meal as well.

No. Sometimes blowjobs are enough.