Since then, over the past 6 weeks, we’ve sort of talked on and off, but it’s gone to her telling me she loves my mind and loves how I think and that it’s sexy. That she cares about me but it’s still “not in a romantic way”.

I feel like if I cut contact with the person I’ve been having strong feelings for and who I can talk to for hours, etc (my ex), then I’d be kind of sacrificing my own personal happiness to suit my current girlfriends desires.

This is called an emotional affair, it's not a platonic friendship. The ex probably isn't stupid either and realises what's going on.... srsly, why would she be okay with OP behaving in this sort of way toward his gf?

that doesn't mean he should throw away a friendship.

For now, he should simply focus on himself and get professional help. His ex is clearly an escape, and becoming dependent on her is the worst he can do.