He may not believe you, but see if he's willing to do proof-of-concept. He says he's telling you things straight up and you're ignoring him. Are these things he wants you to do, problems that he's trying to let you know about, things he's worried about, general conversation, what kinds of things?
If these are things where he wants *some kind of response from you*, then ask him to write them down. Very plainly. In words. "X is happening. I need or want you to do Y please." And then see if you ignore it.
It's possible he's telling you things that simply don't connect to anything you think about or regard as important. That's why he has to be explicit about it. If he's angry about that and doesn't want to believe it, there is nothing you can do but drag him to a counselor so that he can get his head on straight about it, and understand that he is doing something harmful by insisting that you should be able to do something that you can't.