Is it possible for us to have a relationship?

How old are you both? I think you should reverse the roles in your head and see how you would feel. He's made the effort with you heaps and you take days or weeks to call him back, probably made him feel like cr@p and now you're wondering why he hasn't asked you out and appears to be distancing himself from you? What you did to him has major ouch factor!!

That said there may be a chance, he genuinely thanked you for calling him and it obviously did mean something to him. But if I were you i'd certainly start being a really good girl to him (ie: you make the effort) and if a couple of weeks or a month goes passed and he hasn't asked you to be his girl, why don't you ask him to be your guy? He's probably really unsure of you. I wouldn't rush it though, you need to build up his confidence in you again from the sounds of things. Hope it goes well for ya 🙂