Well, maybe. If he is entitled to have his son for the entire next day then y can not dictate the terms on which he leaves him, unless he leaves him in an unsafe situation (like alone). But no more can he tell you how to handle your time with him (say you need to run errands and have to leave him with a sitter as well).  I think the fact that he is leaving him with his girlfriend may be playing in to your feelings here.  He is not "keeping him from his mother" as you put it.  He is exercising his right to visitation.  Keeping your son from you would be refusing to return him at the time designated in the order.  Re-think this for all involved.  Good luck.