Need to vent i guess

Not sure if this is the right place.. but seem to be other people facing similar frustrations.. Have been/lived with my long term gf now 8yrs together. The last couple years have been tough in that she has let herself go and become depressed etc.. I was getting tired of life going by.. Then last november she got a cancer diagnosis, couple months later she said that it was a false positive. I figured this would give her a new lease on life but not the case.. fast forward to last month or so and i told her i needed to break up... she wasn't trying to enjoy life or want to be as active .. constantly tired and depressed.. she wanted to work on it.. so i said ok.. 2 weeks and no difference.. so i said it's over.. then she tells me that she never had a false positive cancer test. and that she has stage 4 terminal that has spread to couple spots in body. So now that explains all the symptons and attitude i feel like i can't leave her, but have spent the last while resenting her. So know i long to be active and live life since have turned things around in other areas during the last 5yrs. I feel like am being selfish, and inconsiderate. I have found someone that i connect with online and is crazy, but with events that have happened feel like that is slipping and maybe not meant to be.. but that connection is so strong. I've been living with the idea of what my gf was like in first couple years of us being together for a couple years now, and now it seems that's all i'll have going forward. As i try to do good by her but see glorious days go by as i sit inside with her.. or while she sleeps. She doesn't want any of her family to know, which makes it harder not that i'm super close with them. I'm in mid thirties and she is in forties. Not to mention anything of the sex life, she has been bitter and depressed for a while now which makes it hard to bring anything up. Would love to have an activity partner.. she doesn't realize how tired she gets.. and i'm just getting things to sink in on the situation.