I need some advice

[×UnaSelvaOscura]

Hi everyone,
It's been a few days that I read daily the things posted in this forum and I wanted to say thank you to everyone of you. Such a beautiful community.

In short I am interested in a person that has BPD traits and I wanted to ask you a couple of questions that could help me getting the best outcome out of this ''friendship'' and eventually other relations in the future.
This person has an high fear of abandonment (once I didn't call her when expected and she suddenly lost any interest in me) but she has an even stronger fear of engulfment and as soon we get really close she completely runs away and after she gets really depressed for a while.
If you see the other person is getting cold how do react generally? If you think she felt abandoned do you give her some explaination or is it better to behave as if didn't happen anything? If you expect she is getting overwhelmed do you step back? How (replying later, writing less, being more cold, giving her days of space)?
All this already happened twice and both times I think I didn't react correctly and she became the coldest person on this planet. In both cases she instantly started liking someone else (anyways she is not my gf) and it's not surprising because she is really beautiful and sensual. What astonished me though is how fast she changes way to talk, to write, interests and opinions about different topics.
In these cases do you think it's better to let her know you are there or to completely disappear letting her ''with'' the other person?

Thank you in advance to everyone.

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[once removed]

i think that the answer to all or most of your questions is "it depends".

we would really need to know more about the relationship between the two of you, and whats going on.

what happened? whats happening now?