I don't know Tyler... but it seems that your ex has been going out of her way to allow the best possible relationship, given the circumstances, between you and your son. She is probably taking the effort for both you and your son's benefit.
Given the courtesy she has shown you, you might find her sympathetic to your feelings. Perhaps there is some sort of face saving compromise that could be worked out. She did ask, maybe there is a way to save this Father's day for you. I bet you could put something out there... but you have to make the call.
Otherwise, lose the resentment, you can't afford it.
Happy Father's Day (My family is gone for the weekend...
, but we celebrate next...
)
Mark