Yes, he does have a right to see his son, irrespective of whether or not he pays maintenance. You can drag him to court for outstanding maintenance, just as he can drag you to court for not allowing him visitation rights. HOWEVER, if the visits are upsetting your child and clearly causing stress for him, you can request that the visitation rights agreed upon, be re-visited. You will be able to ask that visits be regular - irregular visitation is always upsetting - and, if need be, controlled. But you cannot refuse visitation, without warning him to change his ways.