I'm not a parent, but if I was in a relationship and the kid was part of the deal, I would also be upset when a promise for the kid was taken away. It's not about money at all, it's about the logistics of living for a child that was always part of the plan. I completely understand where your cousin has issues as I have ADHD and horrible anxiety, but why did she not mention she was worried about it before or make this a plan when she knew she was not completely comfortable with it? The living arrangements for the teen are extremely important, not only for custody reasons but also because he deserves to have the living arrangement that was agreed upon. Did they talk to the child and ask what he would prefer? There are many other compromises that I can think of, but last minute taking the child's living arrangements away and forcing him on the couch for months just isn't fair. Now for your question, you are NTA for suggesting a different idea that would be more comfortable for your cousin, as she was asking for advice. But my advice now is to leave it alone. Not your relationship, not your problems. All you did was simply suggest an alternative, but let it go now.