Thanks for the update, Goodpal. It makes sense that you'd be questioning the end of your relationship after hearing someone say it was a good thing.
Like Pook075 mentioned, it's critical to understand that just going back to the relationship doesn't fix anything. Walking right back in with no difference in tools, skills, or mindset -- but with feelings of being alone, missing her, and being afraid of missing out -- suggests a repetition of what was broken.
And because you suspect BPD is involved, then traditional relationship mending approaches may also not be effective. It's kind of like taking antibiotics when you have a virus -- nobody would argue that "antibiotics are always bad", it's just that antibiotics won't be effective in your situation.
Let's drill down into these thoughts:
For one I would make sure that I was "all in" and not seeing it as a temporary relationship. This means I would focus on being more emotionally present knowing that I would do my best to be more emotionally supportive when it was needed.
To me, this reads as the "taking antibiotics when you have a virus" analogy.
If being more supportive improved BPD relationships, this board wouldn't be here.
Again, like the analogy, I wouldn't suggest "therefore being supportive is bad". It's more -- let's move to understanding what's effective and appropriate. We have a workshop on
supporting vs enabling that might be helpful, too.
pwBPD have pretty big, seemingly unmeetable emotional needs, that can vary wildly. Many members here share how they kept doing more and more, giving more and more, agreeing with more and more, and doing everything they could think of to be "more supportive" -- but the relationship didn't improve, and, in fact, got worse.
Maybe a more effective approach to the "supportive" question could be:
Can I be OK with supporting at a level that I, from inside myself, have integrity about, regardless of how it's perceived?
If you suspect she has BPD, then she will almost by definition suffer from distorted perceptions. Relying on her perception of "did Goodpal support me enough" is relying on a disordered person to take the lead in the relationship. Getting a stronger sense of yourself, maybe with help and feedback from a neutral third party, may be critical in a second shot having a chance.
This may involve letting go of wanting to control outcomes. Can you go back into this relationship, choosing to care for her in a way that allows both of you to be separate adults in charge of their own feelings (i.e. not overfunctioning/oversupporting), and be OK with if she chooses to exit?
Also, when mood shifts occurred I would stand my ground and set a boundary stating I'm not going to allow this. The hard part for me though, the main reason I needed to leave, was the constant guilt poured on me every time I didn't respond quickly to a text, told her I needed a little time on my own, etc. The day after we broke up it was just refreshing to have my head space back again. We were in constant communication and I felt so wrapped up in her world I kind of lost myself. I would have to figure out what to do about that.
Let's dig into
true boundaries a bit.
Sometimes there are misconceptions that boundaries require you to tell the other person something (like, "If I don't explain to her that I won't tolerate yelling, then I haven't set a boundary"). There are other misconceptions that boundaries are ultimatums, statements, or explanations.
Boundaries don't require the other person to listen or do anything. Boundaries are rules for yourself about what you are OK with letting into your life, and they are 100% under your control.
I think it's great that you are figuring out what you would do about taking time for yourself

Maybe we can brainstorm some boundaries around that?
For example, a misconception would be that you have to ask her for more space.
If you already know about yourself that you need time for yourself... you don't have to explain it to her, or ask her permission. You are allowed to text her "I'll be busy until 5pm -- I will be able to respond to text again then".
And then that's where the rubber meets the road, because even if she texts you again 100 times,
she isn't disrespecting your boundary... your boundary only needs you to respect it. If
you don't reply until 5pm, then you have respected your own boundary. If you choose to reply to her, then you've disrespected/broken your boundary.
Does that kind of make sense -- that only you can set rules for yourself?
So what would sound do-able in terms of you caring for yourself by taking time for yourself? How might you phrase it to yourself, in a way that isn't asking permission from her, or making ultimatums? What rule do you have for yourself, that's 100% under your control?