Step-Father. Before taking on the father role to fullest extent, he should have factored in the possibility and likely eventuality of the bio father and/or the kids wanting to rekindle their relationship.
Demanding to share the 'father & daughter walk down the aisle' process, shows he's emotionally distraught and trying to justify to himself all those years to spending money, time and love as worthwhile.
Him reneging one the rest of the wedding expenses, was him trying to salvage some dignity and self-respect, as he clearly feels duped and hustled.