So glad to hear from you @Bumblebee2 !
Welcome to the forums and welcome to the BPD world! I know first hand what you are talking about.
So many people I adored and pretty much sucked the life out of... then because of sometime small (e.g. they looked at me the 'wrong' way), I completely flipped, lashed out and hated their guts. Sound familiar?
My life was like this for over a decade. Hence, I didn't have friends my age. I only had older people who were ready to 'put up with me' and my rages and adorations...
My BPD was so acute that I eventually got accepted into a BPD clinic. I had intensive MBT therapy where we practiced mentalising. That is thinking about out emotions and the emotions of others. By unpacking this each week in a group session, as well as having an individual session, after 18 months, things began to shift.
The main thing is to teach yourself to pause before you react. The more time you wait and delay reacting, the less likely you will need to react.
At the same time, set yourself boundaries so that people do get smothered. e.g. I'll see that person for 2 hours then I'll go home. That way, you don't fall into the trap of being overbearing.
I'm speaking from a borderline's perspective. This is what worked for me. It may not work for you, but I thought I'd share in case you were interested.