You don't mention what your dad wants or what he thinks about your and your sister's relationship. Or if he even knows about the tension between you two. In a perfect world, of course, you would be able to talk to your sister and reconcile. It doesn't sound like that's possible, though. So, assuming he'd like you to be with him on Father's Day no matter what your relationship is with your sister, while you do want to honor your dad, you don't want to do it at the expense of your mental (and physical) health. So probably the best course of action is to visit with your dad briefly (if you can get there before your sister and have some private time, all the better), and leave if and when things get uncomfortable; but not before you invite your dad to do something with you alone at another time.

Pray on it and then follow your heart. The solution that gives you the most peace at the time and something you can live with tomorrow, will serve you best.

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