You're welcome for the tips.
I believe that you are correct, she is affecting her partner search, that is why I suggest you do it with her, to encourage her to move on. I believe that she is picky, because she wants to keep you in her hip pocket so to speak, so when one of these Tinder guys do not work out, she can fall back on you, she is counting on this.
She does trust you for now, and you are likely her FP (favorite person) when she is telling you she wants you by her side forever - this is her truth, at the moment she said this.
However on the flip side of the coin, she is treating you like 'trash' and being so secretive - she is likely burning the candle on both ends - you're likely the 'side dude' and fail-back when the other relationship(s) fail.
The problem also is I probably also have issues of my own like lack of self esteem etc. I always came back to her because somewhere deep down I feel she has a good heart and I can feel a child that is hurt in her. But I don't think I can go much longer cause my own sanity is on the line here.
I am glad you made this statement, I think you are right, I know I have my own issues that point to codependency. Your perception of her being a 'hurt child' is likely correct too - borderlines have wonderful intentions; however, they do have the emotional maturity of a child and will lash out at the ones they love or care for the most.
Since you have said all of this, you need to consider doing the 'rip the band-aid off' approach a bit more.
Like EyesUp indicated, he gave a few pointers on how to rip it off, it will be painful, and if go this route, make sure you have a safety plan in place, as a pwBPD can snap and possibly get violent (about 50% chance), a safety plan be found at
https://bpdfamily.com/pdfs/safety-first-dv-1.pdf. If you are going to go this route, take her out to perhaps the first place you met on a date (full circle symbolism) where there is a lot of people (witnesses) and give her the bad news then - be tactful, and end the relationship there with softer language.
She will likely claw her way back, and then you will need to use harsher language if she doesn't get the hint - I had to do that with my previous BPD relationship back in 2000 - she did not get violent; however, she pulled every trick in the book to get me back by feigning a heart attack, so I had to bring her to the emergency room until they determined it wasn't, and that is where I left her - sounds cold, but sometimes you just need to cut the rope to save your own
$$.
I know you mean well, and you are a good person, and don't want to do this (otherwise you wouldn't be asking here) - so please think about what I have said, and I would like to know you opinion on it.
Good luck, keep us up to date and let us know how it goes. If you still have questions, please ask.
Take care.
SD