What the heck should i do?

so im practically 18 years old and my boyfriend seems to be VERY overprotective..its kind of ridiculous if i say hi to a guy or if im around my brother and a guy and im talking in a conversation with the BOTH of them he thinks im hitting on that guy or that he questions my intentions. its so obnoxious and i cant find myself to leave him 1. because he's a great guy aside from that fact 2. he cries everytime i try to and 3. i guess im afraid to be alone?? ive been with him for almost 16 months and the allegations or whatever you call them still haven't let ten up....plz someone give me advice!!!