Her likely body was found. The groom to be hasn't been making himself available, and it seems extraordinarily unlikely he didn't kill her.
The boyfriend is following his counsel's advice, and I don't blame him for not talking to the police. Even if he is innocent and knows nothing about the circumstances of Gabby's death (assuming the recovered human remains are conclusively identified to be the missing woman in question), talking to the police will almost certainly do nothing to clear his name, and whatever he says will only make him more vulnerable to prosecution.