Any advise that could help sudden crisis/meltdown that occur due to attachment issues and "minor" problems (ASD adult)

I'm an adult with autism, as well as that I have a few trauma based mental health condlitions.

Despite this I work and live a fairly normal life.

I'm still on the waiting list for appropriate trauma therapy, and my gp can't understand why anyone would need support for the ASD side of things. 

Anyway the mental health and neuro divergence means my attachment issues are not great. I don't want to be close with most people and that is fine. But I have one friend that is a favourite person, and my attachment issues with her cause problems. She is great and really supportive with all of my conditions.

So problem is if anything upsets me with this friend I go in to complete meltdowns and often end up in crisis and wanting to or acting on urges to self harm or yeet. And the thing that upset me and trigger all of this could be something like her not replying to a message soon enough,  or her canceling a day we are meeting. Or one of us unintentionally saying something that upsets the other.

Logically I know it is a complete over reaction to such minor things. And usually I'm pretty tough.  But nothing I've tried calms me in these situations until the situation itself is resolved. For example for me I have found compromise useful to feel in control of the situation and feel it is resolved. (E.g. We cant meet up this day but we will meet up tomorrow instead)

However sometimes compromise is just not possible immediately. And Logically I understand that. Though my emotional mind definitely controls my brain in these situations.

I've tried using my calm box, and distracting with hobbies i enjoy and other calming excercises but in these particular nothing gets through at all. It's like the problem is the only thing that matters in the world and the whole world relies on it being fixed. And i can't do anything till it fixed.

I've tried asking mental health teams for advice on this but none of them seem to understand nor have any recommendations. I'm hoping someone here has some ideas. 

Thanks for reading,  sorry it's such a long question. 

(Yes I'm already under a chrisis management team and am being been referred to complexed trauma therapy team before this message causes to many worries)