He did WHAT.

Oh my gods, I would never just say the conversation was over and hang up on even a long-term SO

I do/did this a lot, but Tamsin is still right. I know you don't like to hear it, but Adam is a douche. I don't really get your fixation with him.

I was in a very toxic relationship once, neither of us were good for the other.  I had my own issues and she her's.  It didn't work out.  However during that relationship she and I shared a lot of culture.  I took from that my love of British comedy and drama.  I took from it a bit of skepticism and a few other things.
Ultimately the relationship was not good for either of us.  However I would say neither she nor I were bad people, just that we had issues.  What I'm saying is, that sometimes, you can have something which isn't meant to be and is better ended then continued--but still have within it some bright spots.

I usually felt like I was being emotionally blackmailed. Sometimes we'd discuss an issue so long that it got ridiculous, and I'd want to go and sleep, or at least postpone the conversation to a time I felt more prepared. Sometimes I just didn't want to have an in depth conversation about feelings for the umpteenth billionth time. Sometimes it felt like we couldn't resolve things at all, and I didn't value the relationship enough to try; I'd just be like "wow, this is an awful lot of effort for someone I'm not really in to, I guess I'll just hang up and ignore them until they stop calling."

Usually I was unable to negotiate an end to the conversation peaceably, and only hung up because I decided I wouldn't negotiate with terrorists.

Oh, and this is not sarcasm (except the last part) i'm genuinely interested in why people act the way they do

I've been lurking in this thread, interested to see what would come of it.  I used to have similar problems, because my family communication style was largely "don't say anything that might upset anyone, ever".  It's taken LONG years of practice to move past that and into being able to say what I need to say.  I still spend a lot of time composing my thoughts and understanding exactly why I feel the way I do, before I say much of anything.  Hence my late entry here.

Speaking as someone who's been in an abusive marriage, as well as other iffy relationships, and as someone who thankfully managed to break that pattern:  This Is Not Good.  He doesn't sound as bad as my ex, but he has largely the same issue:  a complete and total inability to understand that there are different ways of perceiving things, coupled with a complete and utter disrespect for anyone who fails to be him.   Doubting your word in regards to your internal life (opinion, self-perception, etc) is disrespectful.  Hanging up on you is disrespectful.  Raising your competitive streak as a fault (it seems repeatedly) is likely disrespectful, because it can demonstrate a sense that he's above you and trying to correct your faults.  Unless he can take it as well as he dishes it out, it's not right.  

My first husband could be quite charming when he wanted to, but used to shut me down in a similar way whenever I disagreed with him.  He'd also make me doubt my own perceptions (such as whether or not he was snuggling that one houseguest on the couch while I worked late in the other room one night), and would belittle me in myriad subtle and unsubtle ways.  I think as a result, I couldn't afford to give up a millimeter of ego - I became stubborn.   I wouldn't change even bad habits, because they were pretty much all I had of me.  You might ask yourself if you aren't getting more stubborn because of a similar dynamic.  

I used to tell myself that "I didn't have it so bad - lots of women were in worse relationships.  At least he never hits me".  I used to tell myself that "I deserve this because I'm also not giving him what he needs, so I guess what goes around comes around."  In the end, it was ALMOST convincing enough.  I literally asked my mom to come stay with me for a while, to make sure I stayed broke up, when I finally took that step.  Alone, I'd have gotten stupid and relented - pretty sure.

In between him and my current husband, a few dating experiences - one long-term - got me started on speaking my own opinions - a vital first step to being healthy enough for sexual activity.  However, it took until I met my husband to really GET the whole mutual respect thing.  I don't want to go into the whole dynamic of our marriage, but suffice to say that we two rather different people manage to make it work for one main reason:  we trust that the other is trying to do well.  He's a very outspoken sort, and I'm a lot less so, but I'm not actually intimidated by him.    If something bugs him, I'm going to try my best to make it better.  I might fail, but I'm not going to dig in my heels and do it my way come hell or high water.  That response comes from my respect for him and myself, and his respect for me.  Since he leaves my ego intact, it's a pure pleasure to try to make his life better.  I'm a long way from always succeeding, but hey, some of the stuff he does bugs me, and he knows it.  However, we each DO try our best and are considerate of each other's feelings and preferences.  I don't have to camouflage my intentions, or talk around important stuff, because I know that honesty will be returned in kind, and that we'll be able to figure out what works for us.

Short version:  I would suggest that, while you may indeed have some nervous issues that contribute, a huge part of the problem you are having comes from an unhealthy dynamic.  It doesn't have to mean he's a jerk or you are - I don't know either of you nearly well enough to make that call.  It does mean that the two of you together don't work.  

As far as learning to communicate, it will take practice, no matter what relationship you are in.  You may have to write things down sometimes, at least while you are learning.  You may have to learn to say "I need some time to think about that," and "I'm really getting upset.  Can we finish this another time?"  Then DO finish it.  Don't walk away and avoid it.  Walk away, calm down, return at a good time for you and the other person, and speak your mind.  Listen to what they say, and respond as best you can.  Eventually, the gaps get shorter, and you learn to be able to respond in real-time, from the heart.  

I hope this ramble through my exhausted brain has something useful in it.