Boyfriend is driving me nuts?

We've been together for almost two years now. He's 22 and I'm 18. Yeah, there's a four years age difference between us but that's not I'm going to talk about.

So my boyfriend is a sweet guy. He's extremely dedicated to our relationship. He does what he think is best for us, ie, after high school, he had no intent in furthering his studies and in fact he was helping out his dad with a low salary job but after being in a relationship with me, he was willing to be far away from home (and me), alone, across the country to get his degrees. He said that he wanted to get a better job because he doesn't want me to live in a poor condition. He's also a spontaneous person, he can make lovely surprises, he gives me the warmest hug and he KNOWS how make me smile and laugh just seconds after I get mad at him.

But the problem is, he's a very jealous person. Once, before we started dating, I messaged this dude that I used to have a crush on on facebook. A few months later when we started dating, my bf insisted on reading my inbox and when he read our message, BAM he was mad as hell. He said I was cheating on him and started saying sh1t like "I know I'm ugly and I'm not as handsome as he is, just go with him if you want to" and it made me cry a lot because I love my boyfriend and that message was so long time ago yet up till today, when we have ugly arguments, he'd bring that sh1t up again.

Sometimes he's just really irritating. You see, because we are always far from each other, we filled the gap with texting the whole day. Not literally 24/7 but whenever we have our hands free. Earlier today, I was texting him and I heard a text from him coming but I didn't instantly grab my phone because I was folding my clothes. When I replied his text FIVE MINUTES later, he got mad. He became suspicious and even when I told him the truth, he was all like "I don't believe you, you must be texting some other guy" and I CAN'T EVEN WITH THIS GUY. It was FIVE MINUTES, FIVE FREAKING MINUTES, and he exploded. I told him the truth yet he ignored my explanation and still bombarded me with stupid accusations. And of course I get mad too because just because of me making him wait for FIVE MINUTES, this whole sh1t came up. It's ridiculous!

And just now we talked over the phone and he's like, "Let's make it up again, OK?" but I was still pissed at his attitude and I talked coldly and he's dissatisfied that I'm still not okay and expects me to just brush it off too. I told him "Well, I'm not a robot, I can't change my feelings in a few seconds just in a snap," and he replied "Well how about me?" Then he began talking about me seeing/texting other guys. I snapped and I get mad and then he's all "I'm disappointed with you"

WHAT THE HELL IS HAPPENING?! Can someone help me out? This scene had happened over and over again and it's really frustrating me!