It sounds fake to me.
I've known a couple diabetics who took insulin. It's obviously never a great idea to miss your injections but it's not going to put you in a coma to miss one.
Not taking it because she's pregnant? I guess she's never heard of gestational diabetes? Pregnant women can take insulin. I don't know how far along she was supposed to be, but if she had had even one doctors appointment they would have councilled her on how to manage her diabetes while pregnant.
If it was as serious as the "boyfriend" says it is, why he's texting this girl's online friends I don't know. If that was me, I know my partner would be by my side and with my family and our son....Not texting my online friends even if from the hospital. "she's not breathing?" yeah, total cry for attention. If someone you loved was in a coma and on death's door, would you be thinking of playing around with your cellphone?
"i have nothing to prove" pretty much a 100% guarantee that she's fake. It really means "i'm fake but don't call because I can't answer or you'll know i'm fake."
if you know what city she's from, I would call the hospital and ask to talk to her/leave a message (some hospitals won't let you talk to patients). See if she's even a patient.