Hi. I just endured a 3 year LDR with a dude like this. Reading this made me feel a bit sick because it was so similar. He steadily declined as our relationship went on and it could be exasperatingly unbearable at times. His break up speech was one of the most pretentious monologues that I've ever read and actually really had nothing to do with our relationship, it was all about him. He essentially broke up with me to go save the world and find his bigger purpose because our relationship was too small time. He gave such a long self-indulgent speech to my father about why he was ending it with me that my dad couldn't end the monologue for long enough to get him off the damn phone.
Really all he does now six months down the line is sit on the internet being a douchebag to anybody that will listen, and tell everyone else that what they've investing their time in is beneath him and they should find a larger purpose (while he sits on the internet all day, does a part time job, and takes a few classes just the same as them).
My ex actually felt he was above those who had taken philo101 because he had self studied through the internet. He knew enough of the basics that, like you, when he started talking about it I felt out of my depth and it made my head spin. He knew enough to argue and actually fall out for long periods with his friend who had taken philo101 at college. But probably not enough to level with anybody who knew what they were talking about. He used to lie about his school grades and his SAT scores in order to intimidate people. Don't get me wrong the dude was fairly smart, but too fucking lazy to ever make anything of it and just uses it to criticise and hate a world that apparently he's far too epic for. I honestly hope one day he gets out of his bitter funk because before this became his full time occupation, he could be really sweet, was a great cook, and is amazingly crafty and really down to earth (there was a reason I was with him originally, and like you I felt this loss really heavily when he began to change).
What's interesting is the power imbalance doesn't seem to play a part here. In my relationship I was actually the older one, he was fresh outta high school. I'm at a pretty prestigious university, do a degree that's no joke, and I'm way past 101. But he wasn't interested in intellectually levelling with me at all -- if I wanted to discuss something intellectually that I was interested in but he had a relatively low knowledge of, I was cut off. He was only interested in "discussing big" shit he could stomp you down on. It really is an inflated ego thing. And y'know, my degree is about helping the world and shit. Lame in his eyes.
I too was subject to the small talk being a waste of his time. That our relationship took second priority to "finding himself". Blah blah blah. I began getting squeezed out of his life bit by bit. It was horrid, and ugly, if I'm honest.

There is a high possibility it could be a phase. Although this was a running theme with my ex he was also just generally a very intense person who went through just as intense burning passions that eventually passed after a few months and sometimes I just had to grit my teeth and ride them out (one was fuck social relationships they're so unimportant, deleted all social networks, had no phone, that one was a bitch but it didn't last). It's great that your boyfriend is intellectually engaged but perhaps when he moves past the 101s and explores some different areas (and gets over his special snowflake syndrome) he'll be just as intellectually engaged in those, and it will turn out to be something that's more accessible to you that you can also discuss. He's been steady in the past and he presumably has his merits. Try to ride it out and see where it goes. All you can really do is explain to him that although you'd love to hear about what he's learning about and how excited he is about it, he can't expect you to enjoy engaging in a debate about something that really, you have no clue about or really any interest in. Just like if you suddenly wanted to debate on who was the hottest in 1D, he probably wouldn't give a shit. C'est normale.
As many have said it the freshman syndrome is pretty common and fingers crossed you can endure the rock to the boat without it doing that much damage. I can guarantee that he's bringing this level of assholeness into the other relationships in his lives also, and someone may eventually bring him back down to earth soon.

But, honey, no matter how many classes he takes please never forget that you are not inferior to him in any way. You sound pretty down to earth but never let him tread you down just because he has a leg up on the next stage of his life. You're following close behind him, and even if you weren't, your day to day life is still important. You're still a human being that matters just like he's a human being that matters. Nothing gives him the right to talk down to you and make you feel like it isn't. Giving a shit about each other and good communication is the foundation of any relationship, whether you discuss philosophical principles or not.

Also alright, your self love should always come first that's a given but your relationship should still be one of the top priorities in his life. If you feel like you're the only one pursuing it please don't pursue it until it destroys you. I know it can be so hard when you start to feel second then third then forth priority and believe me. It's not worth it. If it was important to him he would make it a priority, no matter what. He has to understand everyone has a line that they can take and he can cross yours. Every relationship has a certain amount of maintenece that you have to do in order to y'know, actually be in one. If he lets this fall by the wayside too much he'd be even more of an idiot if he didn't realise this would mean that he would lose you.

I hope he sees past his big fat head and it works out. If not trust me and everyone else when we say that a few years down the line he'll look back and think, fuck. Even if that's little comfort. If my boyfriend turned back into the beautiful person he was when I met him things would be different. But sadly he's become too dark and twisty for that.