This is an oddly similar story to the relationship I recently ended. Like word for word how my ex would explain our situation. Maybe she was having “tantrums” because she could feel your resentment. Maybe without knowing, you treated her differently and she didn’t know why because you kept it going. My ex always wanted to stay together and he always wanted to make it work but I could tell something was different. He would never openly talk to me about his issues like not having sex with me, but I encouraged him to talk with me about it or work on solutions. if I asked questions about it I was quickly shut down. I could feel the rejection from not being wanted physically and emotionally. I wouldn’t throw tantrums but that’s what he would have called my reactions to backhanded comments or or opinions that were hurtful in my eyes dealing with the feeling of rejection all the time. We never talked about anything serious and I am clueless to why. I did everything I could to be a good girlfriend to him and it was never enough to make me feel how I did in the beginning. When he started to not include me in events or even conversations with his friends even though I was in the room it just reassured me that I wasn’t good enough. I ended it with a lot of resentment towards him for stringing me on for so long and making me feel like I was going nuts because he was constantly trying to make me brake up with him, but still telling me otherwise. Stop being selfish and tell her the truth. She deserves to be happy. if you don’t want her I’m sure she will find someone else or just be happy not being with someone that is her “friend”but not a true partner. I could have put so much of my energy into my happiness but I wasted it trying to make someone else happy. I feel stupid after 5 years of dating and being best friends just to find out he didn’t really want to be with me at all. And maybe you just think she is totally dependent on you. People are a lot more resilient than you think. Maybe without you she will grow into an independent happy person.