Sorry if this turns out slightly too long but desperate for advice 
My baby boy is 4 months old now and I split with his dad when he was about 2 weeks old, I ended it as I was so unhappy and had been for a long time and it was a volatile relationship full of constant arguing. Once my son arrived I knew I didn't want this around him. We were unmarried and never lived together. If anyone is wondering why I had a child with him it was VERY unexpected. I had breast cancer 10 years ago aged 29, had chemo etc. Then developed endometriosis a couple of years later and it was thought I could never get pregnant again (I have a 19 year old daughter) so after 4 years of been together and nothing happening it was a big shock to be pregnant. I coukd NEVER have an abortion so went ahead but decided to end the relationship.
Anyway my ex is now very bitter as we are not the family he thought we were gonna be. He has always seen my son and has him both days on a weekend for a few hours each day and has done since he was tiny. My son has been poorly for almost 2 months, started with a bad cold and cough then developed bronchialitis which have been at a&e around 4 or 5 times over a few weeks and have even had my ex with us a couple of times. Bearing in mind my son is only 4 months old so this has been half of his life he has been ill an there has been certain days I have told my ex my son hasn't been well enough for him to have him that day so the access has maybe been a bit erratic past few weeks. There has been lots of nastiness an arguments via text over the last few months so things were already hostile. He has now told me he has seen a solicitor an will go to court if need be as he wants official days an times put down, wants overnight stays? also wants him for a week or more in the summer and has said he wants alternate Christmases. Says his solicitor has told him he could take my baby now for overnight stays if he wants even tho he has never spent more than a few hours at a time with him, doesn't know when to change his nappy and often brings him back soaking and has brought him back in pooey nappies at least 4 times. Doesn't know how to settle him when he's screaming his answer is just stick him in the car an take him for a drive. When my baby was days old and we were still together he sat up evety single night drinking while looking after him. He drinks every night it's 1 of the reasons I ended it aswell, he also smokes weed an has done for years. Says he's stopped now an won't do it again but that's cos I have brought up drug tests if going to court. I do not want my baby staying overnight with him when he can't look after him without a can in his hand. I have said I think both days on the weekend is acceptable an it's only cos my sons been ill for so long it's been erratic. I also said he could see him a few hours Xmas eve, a few hours Xmas morning then me have him afternoon an he can have boxing day. Said he will not budge on alternate Christmases. The thing eith my ex is he is one of these know it alls an likes to be right so its very hard to reason with soneone like that.
We have to attend mediation first before any talk of court. It's gonna cost thousands to drag it through court and I am at the moment on benefits. I have a meeting with a solicitor on Friday which is costing £120. It's gonna cripple me. I don't know why he's doing this an can't just be happy with what we were doing. I wouldn't mind overnight stays when my son was much older and could understand more but I do not trust the man with my baby overnight not when he is clueless what to do with him and the fact he drinks while looking after him. He is just totally bitter am feel he's doing this to get back at me in some way.
Just want some advice from anyone who has ever been through the courts for this and what is usual access courts grant to father's in this situation. My son has never left my side apart from when he takes him a few hours and he screams sometimes then probably wanting me. He wouldn't cope a night away from me. Can anyone advise ?