15 weeks pregnant and suffering

I was a bit suprised seeing that positive test considering i was taking birth control. I have a 3 year old and 1 year old who i love so much but a spouse that a really cant stand anymore. Our relationship has been over for quite sometime, but the guilt of breaking up my family, and being financially unstable has kept me here. Well there was no way i could have an abortion, i had one when i was 18 and would never put myself through that again. So i decided to keep baby. Everyday i have this overwhelming depression and got diagnosed with perinatal depression, prescribed prozac, but havent been taking it because i wouldnt be able to forgive myself if something happened to baby from it. I feel horrible i know there are woman that would die to be me, but this is the way i feel and i cant help it. Im just counting down the days i remember being happy with my other 2 kids during pregnancy. This one im just like, how am i gonna make it to the end! Im miserable! I have talked to my sister about possibly adopting baby because if i feel the way i do about it now, how bad will ppd be? What if i cant take care of baby? but im scared to commit to something like that when it could just be insane amounts of hormones causing me to feel this way. Anyone feel this way during pregnancy? Wil i love baby when it comes? Please no bashing me im just looking for love and support right now im a pretty dark place mentally.