My daughter has recently moved in with her boyfriend, they are going to move out of the place they’re currently in and get their own flat together. The boyfriend earns more than twice what my daughter earns as she is currently studying and will then be training. However, he is insisting on splitting the cost 50-50, I think this is unfair and they should do it proportionally. I don’t know what is the normal rule of thumb in these cases, how do your adult children split their living expenses with their partners? They are in their 20s, they are not engaged but there is every indication that it is a long-term relationship as they have already been together for three years and have talked about getting married in the future.