To me her ex seems like a guy who likes a fan/motherly girlfriend. The kind who adores, supports and looks after him but doesn't place expectations on him. Essentially a rather selfish kind of person. He wants someone who supports his dream and gives him the freedom to fully pursue it but seems to lack interest in reciprocating that. We'll have to see how things go, he may just be using her or he may like her, but he's not one to make sacrifices for her sake.
On the flip side though I think the MC didn't help that mindset. She's easily enchanted by him so she's quick to cave to him. He's gotten used to that as their normal. When they broke up it probably was a real shock to him because from his point of view things seemed to be going well and all of a sudden she has this other future she wants that he doesn't fit into. I think their relationship was less a partnership and more of her orbiting around him.