It isn’t a good to know that you was upset. I think that your cousin and her boyfriend should adopt to each other way of living. So it might be hard to the start but it should be ok later on. i know it is hard to live with someone, but only time will tell. Hope your cousin is ok.
A couple can live together happily, but there are some changes for both side of the relationship to allow them to live together. i think that they love the person the way their are, but maybe thery are not ready to live together.