Why are people so against dating more than one partner? Aside from STD worries, I don't see anything against it. Thoughts?

Jealousy.

This OP... Fucking duh... It's really hard to get completely rid of jealousy. Even total swingers have problems with it.

Because you just can't.

This. I would never be able to share the boy I love with another person.

That being said, some people might disagree, in which case they can certainly go for open relationships and I don't see a problem with it.

this partly, also the fact that how could she be my "one and only" if there are other people.

Do you really need a fucking reason?

There is no good reason. It's just natural. When you're in love with a person, you just can't stand to see that person with someone else. They're yours and yours only. If you couldn't understand that then you'll probably never be loved.

this exactly.

People are too weak to control their emotions. This is why most people can't have a healthy relationship in general. The ironic part here is that if you couldn't keep shit together in an open relationship, you're going to fail in all relationships. If jealousy can drive you apart over such trivial things, even if neither of you is actually with anyone else, the idea of it will destroy your ability to properly love someone anyways. When you're truly in love, such ideas or even actions can't destroy those feelings. Anyone who doesn't agree, hasn't really loved someone, but rather loved the idea of possessing someone.

What a stupid fucking post. Not wanting your significant other to get fucked by 17 different people doesn't make you some possessive freak. Part of loving someone is being devoted to them. Can't do that when you're both hooking up with others.