You gave alot of information, but im sure theres alot more then what you said...
But from what I can tell you were in an abusive relationship...abuse ranges beyond verbal or physical.
Her threatening suicide if you leave is a huge signal of an abusove person...she was mentally abusing you.
I will take a shot in the dark and say your parents were probably abusove aswell....you mom got mad when you had an asthma attack!?
Feeling guilt and helplessness as a child!? You were a kid...your parents should take care of you...NOT the other way around!
Sounds like you suffer from a cycle of abuse...suicide is not the issue it is only a symptom of a bigger problem..if you dont get help and focus on your co-dependency and pattern of falling into abusive relationships...you will continue finding other manipulative people who will only bring you down. Its a circle that you need to break. You can not control others happiness, only your own. Let people think what they will about you and try to stay true to yourself.
This girl wasnt suicidal...she was seeking attention and it worked on you....people who are suicidal dont go around screaming to all who will hear, they sit silently in their room and take their life or at least try.
Life is hard...we make bad choices, we get hurt, people let us down...we can either fall into the spiral of depression and let it consume us or we can rise above it and try to make a difference. The world is a big place where people are suffering more then we can ever fathom...no matter how hard we think we have it there are others going through worse...
We all have the potential to be someone great...even if its just to one person...but you have to believe in yourself first and avoid those people who seek to bring us down....surround yourself with people who are happy, people who lift you up, those who want to be in your life without an agenda. When you surround yourself with people like that you will find yourself happier amd capable of great things.
Good luck with your future...know that you can and will and just do it!
Sry for any typos im on my phone