Why is he so inconsiderate?

i have been with my boyfriend for 6 years now! he is 26 and i am 22, i just wanna say first he does have a very pure heart but i just wish he would show it more. He is very stubborn and quite a closed off person and not a great communicator at all, things have been very unstable for a while now, whenever we seem to have a tiny disagreement or argument he seems to be very inconsiderate if he has hurt my geelings in any way. For example even if i cry in front of him because he is being inconsiderate about something he wont comfort me and hold me or do anything. Instead he puts himself first and defends every single thing i say, and this is happened near enough our whole relationship, i do admit that i sometimes might over-react or get over-emotional but thats only because he provokes it and im just sick to death of the way he treats me and im sick of feeling trapped as i love him so much but at the same time i know i deserve better then this and find it so hard to leave him because i would love things to work out but...He just wont take any responsibility for his actions, instead i have to end up trying to be the bigger person and apologising for his mistakes just because i dont want the argument to linger on for days, because normally he will ignore me or wont contact me for a good few days, and this is just so hard on me, and very selfish on his part. I have tried talking to him about the way he acts towards me but he said its just who he is and that he likes his space a lot so he can think about things. We made a compromise the other week that he would only leave it one day if we had an argument but he didnt follow through with it cos recently we had a small argument and again he didnt contact me for a few days, i eventually got through to him and he said its because hes "unsure" about things, and im thinking well shouldnt it be the other way round with me feeling like that? hes probably had enough of all the arguments and stuff too but seriously, if he was more considerate and just took responsibilty more for his actions half of our problems would not be here.....