I’ll leave you with this OP, you need to have a discussion with your GF about where the line is for both of you with how much you are prioritizing this particular friend especially given the background. Even more so since your GF has been cheated on before.
The fact that you are prioritizing your friend after already crossing the line with her multiple times, and failing to set even a single reasonable boundary, would be a massive red flag for me. Actions speak louder than words. Think about what actions your GF is seeing, that will matter more than you just telling her you “love” her. Your actions are also leading on your friend and indicating (to her and multiple people even in this thread) that you are open to a romantic relationship with her.
I’m a bit older and would have no patience for how much more care and consideration youre showing this friend than your GF consistently. Your girlfriend sounds like she’s far more forgiving of infidelity in a partner than I would be, so she may be OK with still being in a relationship with you while you continue to prioritize someone whose shown a great deal of disrespect for her and your relationship. How your relationship works with this friendship is something you two should probably discuss explicitly.
If OPs GF is really reading this: you deserve someone who will prioritize you over their affair partner.