My ex wants to claim him our 20 yr old student for 2018, since he paid for his college with the GI Bill. I provide his spending $ and home. Who's right?

He is claiming that the money he provides, nothing out of pocket only the GI Bill, makes him eligible to claim my son for 2018. My son lives with me when he's not at school and I provide him all spending money, car, car insurance, phone, clothes, etc.