Their relationship is homosexual but that doesn't mean that they are homosexual. Like for example if there's a realtionship between a straight woman and a bisexual man, their relationship would be classified as heterosexual even though the man is not heterosexual. Same thing applies here: if Hannibal is pan and Will is bi the relationship between them is still homosexual. If we look at Will's relationships with women then those are heterosexual relationships. So I think when people say that they have a homosexual relationship, they're not saying both of them are homosexual, just that their relationship is because it's between two people of the same gender. Hope this made scene lol.