Is it normal to miss him like crazy?

They say that you only miss you first boyfriend like this, cause you get attached to him... but he's not my first boyfriend, and i miss him like CRAZY. I'm at the verge of being obsessed with him, but i'm not-- I won't let myself go that far. But seriously though, in a few hours that i don't see him, i miss him like i've never seen him in a week, a month, even a year... i don't understand this feeling because i think that this is probably the first time that i felt this way towards someone. I'm not worried because i know that he can handle himself, i just simply miss him, cause he's been busy a lot.

we used to be together all the time just hanging out, and that became a habit overtime... but now, we don't hang out as much anymore... but we do hang out, when we can.

explain this to me, please.

i don't know what you call this.
i don't understand this feeling.
what do you call this?