Hi choccybickie
I don't think a court will grant him more than a few hours access to your Son and that may be supervised. 4 months is too young for a child to be away from their mother for more that a few hours. If you are breastfeeding, do not let him force you to express more than you are happy to just so that he can have his son on his own and do not let him give your Son formula if this is not what you want.
Keep a record of all the texts, visits and conversatons, if he takes you to court you can use them to show what things have been like. You are absolutely right to say no to him wanting to take your Son away whilst with other 19 year old. His time with your Son should be just him, and his family, not his mates.
My daughter is 9months old and I will not let her father have her on her own becuase she doesn't know who he is. I have no intention of letting him have her overnight until she is very comfortable in his company and he knows her well enough. I expect he will try to take me to court over this but I have faith that no court will grant an overnight stay for a child under 18months. If he does take you to court, most courts will order you to go through mediation first as they prefer these situations to be dealt with between the parents with some guidance rather than any court order straight away. Stand up for what you believe in because you alone know what is right for your Son. Trust in yourself and your instints.
Keep yopur cool with him, don't let him make you visibly angry, rude or retaliate him with any punishment. Then you will always have the better hand and you will feel so proud of yourself when he realises that you are in control.
The suggeston his Solicitor made is ridiculous, your Solicitor's is more appropriate. Do not let him bully you, I completley understand how he is ruining your time with your Son, my ex did that too and I don't know If I can ever forgive him for that. Try to find some peace when you can, push him out of your mind. I have to audibly say "no" when I start to stress about it. i hope you have strong support from your family and friends. Let them know what it going on, what he is trying to do as there really is strength is problems shared.
George x