Different father’s...

I’ve been needing to get this off of my chest, I don’t have many friends or people to go to but it has been hard on me. My oldest son, K, and current little one in utero, J, will have different fathers. My fiancé and father to J is incredible. He’s been in K’s life since he was 2.5yo, and K refers to him as Daddy because his biological father is not in his life. I have sole custody over K, and bio dad has the right to visit with K. He has only seen him a handful of times this year, and it’s like pulling teeth. He is the type of person to not reach out to me for months but then wanted him on Father’s Day and posts on social media or tells people that I keep him from K, when in reality, I don’t. He was extremely abusive to me and neglected K when he was only a few months old so I left him. Very toxic mentally and physically in the relationship I had with him. It was hard being a single mom, but my family supported me and helped me through everything. I had to change my phone number, make my contact info confidential from him etc because of how he was to K and I. I use an email, specifically made for contacting him, that I save all records of conversations, old texts, court paperwork, support info and visit schedule because if I don’t document literally everything, he will lie and manipulate, because he is a pathological liar. I am so worried that K will not adjust well to baby J. I love my oldest so deeply and have such a close bond with him because we have been through a lot together. My fiancé is so loving and protective of K, and treats him as his own. Some days I wish K’s bio dad would stop coming in and out of K’s life as he pleases, or just completely stop altogether (and the court just let’s him do it!!!). It’s not fair to him and confuses/upsets him so much. I watched my brother go through this with his bio dad and it broke his heart. It breaks my heart now to see my oldest go through the same. This will be a really confusing time having J, and my sister will be coming to help us with K while at the hospital and the following days after. Has anyone else experienced this? How did you manage it? Any advice?