<human>: Usually I would confide in my boyfriend but he is asleep and I am sat here trembling. I've no idea what to do.

Our papa died about 7 months ago (I'm adopted, brother is not)  and since then he has been very very unstable. He has PTSD amongst over things but I refuse to let that be his excuse. He's done many things to me, including trying to get me cut out of my father's will and trying to destroy my relationship with my boyfriend (who is incredible and the most important thing in my life, the only thing that would kill me to lose). This morning, about 3am I got a phone call and answered. It was my brother, drunk and rambling about how he was determined to ruin everything good I have... starting with my relationship. The fact he was drunk means nothing - he always does what he says and he always puts all his effort into everything he does. 

I'm sat here trembling, I have no idea what to do. He has nothing that could hurt my relationship but he has successfully caused massive rifts in the past and makes me so scared and emotional I lash our irrationally which in turn damages my relationship.  None of my other family care (my biological family have little to do with me), they're all wanting a drama free life and won't tell him to back off so I have to deal with this on my own. 

What can/should I do? I don't speak to him, haven't in months and we live in different countries (I'm in the uk, he is in the us) but he travels here often. I'm due to move in with my s/o [27m] in 3 months and will feel safer then but until then I am constantly on egg shells and so sick of it.

Can you succinctly summarize the text in 1-3 sentences?
<bot>: brother is a mental case, vowed to destroy my relationship and I have no idea what to do. Scared. Need advice.