I (18) live in something similar to foster care in europe and I got a legal guardian. 

I was in a psychiatric clinic over the summer and (finally) got BPD officially diagnosed. 

Last week I had an argument with my guardian (nothing serious, about christmas). He said my behavior was inappropriate and unfriendly afterwards. I apologized and told him I had a hard week and due to BPD I can't always control my emotions but I'm working on it. (I had heavy outbursts daily before I started therapy, so I'm normally proud if I'm just a bit unfriendly)

He said my illness isn't an excuse and I still overreacted and he can't tolerate my behavior if it happens again. 

I know it's not an "excuse" but it's one symptom of my illness which I can't control, how do I explain this again? I feel extremely misunderstood and avoid talking to him. Help.