I have a 7 year old son with my ex partner we have a contact order in place for every other Thursday n every other weekend,I want to relocate 300 miles away to be with my partner as we are expecting a child I'm 6 months pregnant,I would still make my son available as much as possible to see his dad I'd just like to know where I stand legally

If you have a court order in place and your move will prevent the exercise of that court order, then you have to either work out a new visitation schedule or get a court to modify the order.

If you move without the court modifying the order you will be in contempt of court and he could use it to get custody of your child.