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OP - I commend your effort to do so much for that girl, knowing she was going through a bad time, but she showed you who she really is, so believe her and move forward without her.
Suicidal gf anon - If it wasn't you breaking up with her, it'd be something else anyway. Depression and suicidal thoughts are persistent demons. There's not much more you could have done for her, and trying to keep her afloat was drowning you in the process. Breathe, treat yourself to something nice, and hope that she gets the help she needs someday.
The both of you should keep in mind that you're not responsible for anyone's happiness but your own. There are brighter days and better girls ahead!