That says it all right there
Sadly, I have been in this exact situation before with an ex of mine.
She probably makes your brother feel like he cant do any better than her and the only way to keep her happy and keep her around is by going on trips and buying and paying for everything with his money.
I bet you anything that if your brother were to tell her that he is bankrupt or has no more money etc.. she would be long gone.
I would not accomodate her what so ever and by doing so, would not help out the brother.
Why dont they move in together if they are that serious and have been togethe rfor 3+ years? That way he would save money on 1 mortage/rent payment at least. If she's serious about your brother why dont they live together?
CBF