What the OP is describing is very much BPD. If that is your only problem, that's great. Don't you try to change too much or you might get much bigger problems. You might wanna see a therapist if you experience worse problems such as longer, more spontaneous (cf. reactive) (episodes of) depression. But don't assume the worst. Your problems in relations may be a protection mechanism which keeps you from getting too (erotomania severe) involved.

The best thing would probably be to learn to talk about these feelings. Ambivalence due to BPD can be treated with psychotherapy or just by you seriously analysing your feelings and behaviour and to see whether you can attenuate your internal turmoil—in a more healthy way.

I have seen people taking care of these relationship problems later in life. Don't fret.

The rest of you sound just like me: hopelessly bipolar.

To be fair, I also have many of the borderline traits, but I couldn't help myself and they turned into SZA/BP problems (although prodromes for that were already present, I just treated them with a BPD personality). Most if not all here should be able to relate.