How to figure out what's wrong?

I've been in a relationship with a guy for over a year, and off the bat it has been very intense. Due to work we've been living together since before we were even together and that had been the case ever since. We've had some rough patches, where we were confronted by how different we are and see the world, but after a year we've gotten to know each other quite well.

However, the past few weeks we've have constant ups and downs. More downs than ups in my opinion. He gets frustrated by all the things I do wrong (plan a date that's quite far away, ask him to stop fidgeting, not ask him to come to a doctors appointment with me because I assumed he didn't want to drive that far, etc). I see that I make mistakes, but if I ask him to just calmly mention it to me instead of attack me and get angry, he, well, gets angry.

I, on the other hand, hate that I have to tiptoe around him. I'm very co-dependent (which I know can be very annoying, so I'm working on it..) and my mood tends to change with his. Because of this, I try to ensure that he's happy and that I communicate as complete and respectful as I can, but the constant fear that he might snap again is taking a toll on me. I'm just not enjoying myself anymore.

I love him, and I know he loves me. He can be so terribly kind and then we have great moments together, but he can also be so hateful and cold.

We've had some proper conversations about my worries and insecurities concerning our relationship, and it makes him sad that I'm doubting it. After that we are usually good for a while and we're both putting the effort in to adjust to each others needs, but it never lasts long (sometimes just a few hours).

I think a part of our problem is the fact that we're always in close quarters with one another, so I'll be spending some time away from home (a few days). He says that it makes him sad I won't be home, but I honestly think all those frustrations are partially because of us constantly being together. We have our own friends and plans, but maybe it's just too much?

However, I think the root of our issues might lay deeper. I just don't know what it is, or how to figure it out. Loving each other is enough for now to keep fighting for 'us', but I don't know how to do that. I can't ask him to change who he is, nor would I want him to ask me that, so that makes me question if we're maybe just too different (and maybe too stubborn). The thought of breaking up makes me sad, but the thought of being stuck in this relationship (stuck also because of our work) doesn't make me any happier. I want to find out what I might be doing wrong, but I can't seem to find the red line in the causes of our fights/his frustrations.

I just want to be on the same page again, because that was so incredibly nice. But I honestly don't know how to get there...