Hi Mr. mister,
Welcome and hello

It sounds like there is no custody order in place? How do things work where you live when a parent blocks access?
A lot of us draw on both therapy, to help with relationship skills, and legal help, so we can offset some of the BPD stonewalling and obstruction that tends to go with high-conflict people.
Are you documenting everything? Whatever else you do, it's a good idea to keep every text or email, and maybe keep a journal, plus track things on a calendar so you have evidence if/when you decide to work things out in court.
When is the last time you saw your son?
When she makes accusations or blackmails you, how do you respond?