Hi, thank you for your question. Firstly, whether you have the baby or not is your decision and if he wishes to be involved in the child's life the child has a right to such a relationship but you will have a right to reasonably refuse if there are child protection or welfare concerns.
Given that he appears to be intimidating and harassing you, if he tries to contact you again you should first contact the police and thereafter consider whether you require an injunction to prevent him from contacting you again - this can be done using form FL401 to your local family court and if he breaches this injunction he will be liable to be arrested.
If he attempts to seek custody of the child, this is not an automatic right for him and a court will need to make a decision based on the full facts of both your circumstances and what is in the child's best interests - bit based solely on the information you have provided, if his mother is his dependant he may find it hard to convince a court that he is also able to solely care for a child.
I hope this assists you. If you found this information helpful please provide a positive rating using the stars at the top of this page. I will not be credited for your question without a positive rating. Thank you