He thinks that he really needs you, and he is afraid that you will leave him for another guy. If you leave him, this would cause him a great hurt, that he wants to avoid.
I think your boyfriend may be so jealous because he wants closure. If you have guy friends and you hang with them that could probably be a problem to him. If he's with someone he probably just wants you by himself. Doesn't want any kind of contact towards another guy. His jealousy shows how much he cares and loves you. He wouldn't trade you for no one.Why is my boyfriend so jealous?
well that's easy when a guy get jealous it only means that he loves you, well we all get our own conclusion when we see our girlfriend/boyfriend together smiling with someone especially when you don't know who is it, be scared when he doesn't care because that may lead to "the end"...How not to be jealous?