Throwaway account, help or advice gratefully appreciated!

Hi, I’m a 26yo M with BPD from the UK.
I take Lamotrigine &amp; Quetiapine and am having DBT privately.

I struggle with a number of things but mainly the relationship I have with my FP, who is not my romantic partner. They are really caring and compassionate and we have a great time when we are hanging out. 

However; I really have problems when we are not together, or that I know he is with other friends. Mainly it’s just jealousy, but I am also terrified he will get into a relationship and that our friendship will change, or end. The paradox is that I love and care about him, and want him to be happy whether that is in or out of a relationship.

When I know he is going out in a few days I get more and more anxious in the lead up. Whilst he’s out we don’t talk (as he’s enjoying himself) but my mind goes haywire - I get a dry mouth, heart palpitations, lose my appetite and cannot concentrate on anything else. 

The morning after he’s been out I get into a right state until I know he’s safe - often I end up “testing” him that he still likes me and that nothing has changed.

Over the past two months these feels have got more and more intense and the techniques I have been learning in DBT (such as postponement, attention training etc) seem powerless against these thoughts. It is now getting to the stage where I am self harming and making loose plans for suicide because I cannot imagine living without this sinking feeling.

I have had FPs in the past and have felt this way. The difference here is that the FPs in the past were toxic and did not care about me, so eventually I came to that realisation and were able to cut them out of my life. The difference now is that my FP is a good person, he understands and cares about me and it is a friendship that is worth fighting for.

My FP is really caring and has a good understanding of BPD, and from time to time we both confide in each other about various things. I am trying to avoid over “dumping” emotionally on him to prevent more dependence.

I am very frightened of what I’m capable of. The only reason I have failed suicide attempts when I’ve been in these states before are that the PRN medications I’ve taken have acted quickly and knocked me out before I had the opportunity to do any lasting damage. I know that I will end up killing myself if I cannot shake this dreadful feeling.