How do I do somethin this big when I’m not 100%

So I’ve recently had a baby 5 months ago. My third child. I’m taking birth control but somehow I’ve just found out I’m pregnant. Now I never ever thought I’d have to make this decision but financially I can’t keep this baby and it is breaking me into a millions pieces I’ve cried for 3 days straight knowing I have to make this decision. It’s the hardest decision I’ve ever had to make and I do know deep down it’s the right decision. It would mean my children have a much poorer quality of life and massively affect them. Me and my partner both work full time but cost of living in my area is unreal and moving is out of the question for personal reasons. However I’m not 100% on doing this but I know I have to. My partner says he’ll support me whatever I decide but I need to think of my family and it’s killing me inside. Anyone been through this? If so does it still affect you? Sorry for the long post.