Both sides happinesses are different, yes. I am happy as a spiritualist as yourself a christian. I assume we cannot see another person with happinesses "based on our beliefs" because to me it makes no sense to not commune with ones ancestors while you likewise but (edit) without god instead, that is fine.
However, whats not fine is to say another person Is Not happy based on our beliefs: we do not know. If they are happy and say so, who am I to judge. Their happinesses isnt depended on my belief (or yours or inchrist) but in that person and that person and his or her faith or values only.
Who has the right to say someone else is not happy because they do not share our beliefs or religion?
(Edit) Or related to the op, our sexual orientation?