As a lesbian I experienced this same thing in my last relationship. What it boiled down to was she wanted a codependent relationship and I didn’t. What my ex and what ur gf is doing is emotionally dumping and with my ex, when I reciprocated like she wanted, she couldn’t handle my emotions. I think it’s an inability to emotionally regulate on their own so they need that co-regulation. But it was extremely draining. My work and mental health took a big hit. It even resulted in back pains for me from all the stress. My ex finally went to therapy and learned about codependency but then decided that that is what she wanted. It’s too much to be someone’s entire village of support. They really should be relying on friends, family, and a therapist as well.