How does he even remember that he has the condition?

Often times, he excuses himself towards other people by saying "I apologize, you see, I have this condition..." when he doesn't know what the other person is saying.

But if he can't form new memories, how does he remember that he has the condition itself, since him having a condition is something that appeared after the trauma?

He should not only keep forgetting his recent memories, but also keep forgetting that he keeps forgetting them. He might feel that something is wrong because he can't remember recent events, but that would always be the first time for him that he would feel in such a way. The fact that he's aware that his memory loss already happened quite a few times and that this is caused by his "condition" seems to show that he somehow does form new memories, namely the very memory of acquiring the condition.