talk to your parents or someoone who is your caregiver!

anyone that says they are going to kill themselves is NOT stable to be in a relationship with and needs therapy themselves. do not get involved with someone saying that or threatening that . it is not right and they need help.
if girl 1 cheated on you several times, or as much as you know, then she is not again a stable person. she needs to find help. you do not need that burden.
resolve what you started. don't cheat. love does not involve games, mind games, threats, depression, etc...

please talk to your parents. i know that sounds really lame but whoever is helpfull in your life you need to talk to.

i think you are too young to have sex. it is too much responsibility! what would you do if she gets pregnant? std? etc.... broken record i am sure but trust me, you are NOT ready.
do you think that this chaos is what relationships are based on? absolutely not. wait to have sex. you have your whole life ahead of you don't do it.

just date and have fun, no need to get so serious ! enjoy life and friends, date a bit and don't get so committed. you are too young.