I've just spent nearly an hour reading through this post. OP I admire you for being honest about your mental health, you are obviously very aware of the effects that has on your life as a whole. I'm not going to advise you on what you should or shouldn't do because ultimately that is your choice, you will have to live with it either way.
Tbh what has driven me to comment is a couple of the PP's. One saying that at this gestation it is not a baby, and one advising you to look at how formed this baby would be now. I can answer that after losing my daughter at 21 weeks and 4 days. She WAS a baby, although skinny she was fully formed, she had all of her fingers and toes and nails had begun to form. She had features, eyebrows, a perfect nose and pretty little mouth, perfect little ears. She was beautiful. Yes her organs weren't strong enough for her to survive but another 2 weeks and 3 days and she would of been helped. It's insulting that people can sometimes be so ignorant and make out that at this stage it's not a baby because it is, she was my baby, my daughter. We had a funeral for her, she was cremated and she's at home with her family who still to this day grieve for her.
OP this is your baby, your body for you to do what you think is best. But those movements you feel everyday, those kicks and those rolls are your baby telling you that they're there and they're ok. I know you don't feel strong enough to do this alone but can you honestly say that you have exhausted every option for help and support that's available? You don't need a partner to be a successful parent, if you want to do better for yourself and this baby then it is possible for you to turn things around. You are worthy of your children and you can admit your problems. People don't judge you for asking for help, it's not a weakness. We can't always run from our fears and depend on other people to bring us happiness, we have to fight for it ourselves. You could shock yourself at just how strong you might turn out to be and what you could be capable of if you just prioritised yourself and your children. It's heartbreaking reading how little you appear to value yourself, I know you've made mistakes but you can't beat yourself around the head with them forever, or keep adding to the pile.
This is a massive decision for you and I'm not in your shoes and I didn't intend on this to become any form of lecture to you, I just hope that you can make the most informed decision that is best for you. You will be in my thoughts xx