I'm really sorry you're going through this- losing somebody who you thought was supposed to be there for you, especially in times like these. And honestly, a good partner would be there for you.
Some partners will run when they hear this because it's difficult/stressful for them and they don't know what to do in the situation. I'm not saying what your gf did is right, but I do understand ppl getting freaked out when they hear the topic of suicide. I went through a similar situation a couple years ago where I mentioned suicide to my gf, and overnight our relationship changed. She wasn't the type of person who was gonna handle it well, and even though I knew it at the time, I couldn't help it because I was trying to open up to her and reach out for help. It also made me realize she wasn't the right person for me because I need somebody who truly understands depression and can empathize and help me through my dark moments. So for me, personally, it was a silver lining that it made her leave, because she just wasn't the person I needed in my life regarding my dark side. It took a very long time for me to get over it, but I'm still here and I managed to get through it.
Idk if that helps in anyway, but I do feel for you :( it's such a shitty situation. Feel free to message me whenever you like and about anything you want.
