hi hun
not much to add really as you've had some fantastic advice, just didnt want to read and run. what an amazing thing you've done caring for your daughter through your illness and all the troubles you've had. i am 7 years older than you and long since finished uni, got married, am a homeowner etc and even with all that stability parenthood has been tough. I admire you so much for having your daughter and caring for her despite everything.
like the others have said, your daugter has to be your focus - if you kill yourself where on earth will she be - she needs you, and she needs you to find the strength to get well. having no partner around to help must be exhausting, on the other side though you can wake up knowing there will be no nasty arguments with him, you can accept you're ill and take your meds and do all you can to get well without him confusing you.
as far as financial things go - have you looked into everything you're entitled to now he's gone? do you have family close by to help with a bit of childcare now and then -even if its just for a bit of down time so you can feel like a human being in your own right.
i know the horrible feeling when you imagine your ex with someone else, time heals though and the gradual healing of your depression will lessen that sickening feeling and the need to cry so much. in time you'll look back on it all as a nightmare from a better place.
big hug and remember you're life is amaxzing - it brought your daughter to the world, and your purpose for being here is to give her all the love you can xx