Define custodial parent please?

If you have "shared" custody, you are as much a "custodial Parent" as he is, given that's a 50-50. You can always consult with family services if he's bulling you and also, make sure some people know he's bullying you because at some points you will need witnesses and having witnesses may actually help you in a sense that if you make strong enough of a case he can lose custody.