What going in my ex's head?

It sounds like he's not really that bothered about being friends, or staying in touch with you. If he did he'd make more effort to keep in contact. The way he says he'd go for a coffee 'somewhere down the line' shows this too. It sounds like you have more feelings for him than he has for you. It'll be better for you if you don't contact him at all. Just forget about him and delete his number. You'll end up getting hurt if you keep trying to make something out of this.