Divorced, ex is custodial but i pay mortgage, insurance, taxes for my home and medical insurance and expenses for son. Do i have any ability to claim him?

It depends. As the child's noncustodial parent, you must be eligible to claim the child as a dependent. The rules for claiming a dependent usually require the parent to live with the child for more than half the year. This rule can be waived however since you and the other parent are divorced.

For this waiver to apply, more than half of the money needed to support your child must come from you and the noncustodial parent. In addition, your child must not live with anyone other than you and the noncustodial parent for more than six months of the year. 

In order for you to claim your son, you will need to get Form 8332 signed by the custodial parent.

Please view the TurboTax link below for more information about this rule.

https://turbotax.intuit.com/tax-tips/family/what-is-form-8332-release-revocation-of-release-of-claim-to-exemption-for-child-by-custodial-parent/L25kdeRnR