The best thing to do is to take screen shots of all these inappropriate posts, and show them to your lawyer to find out what your options are. Do not - I repeat, do not - discuss them with your ex. Do not post anything on her page/wall and do not comment about them on your own page.
Make notes of all the times he said he can't see his son, saving voice mails and emails and texts to that effect, including the date and time you got these. Then give that info, correlated with the FB comments/bragging, to show where he was and what he was doing. Discuss ONLY with your lawyer.
None of us know what's in your divorce/visitation agreement, and we don't know how things vary from state to state.
The important thing is to take the long view here - no reactions out of anger or impulse.