Boyfriend always shuts down

So any time my boyfriend does something wrong and an argument starts about it, he immediately gets so exhausted and shuts down. He will go to bed in the middle of an argument and leave me so upset and sometimes crying. I hate this and I have no idea how to get him to see that there are better ways to resolve conflict. I’ve tried everything, even being super calm and understanding, but he still just shuts me out. When I say shut me out I mean I will be trying to work it out with him and he literally will not say any words except the occasional sorry. Keep in mind I’m generally a very calm person so it’s not like I’m screaming and berating him. I can’t keep having arguments like this that are so small yet ruin our whole night and most of the day the next day because we went to sleep angry. The day after this happens he is typically very remorseful and just says “he was tired”. Any advice???