You were, are, his lover, and Lydia's older brother.

However, he angered a witch, which led to her cursing him, or, in technical terms, you. To forget his name, and face, so you could never summon him again, and only be haunted by the memories he left behind. Torturing you both, Beetlejuice only being able to watch his lover from afar in the neitherworld.

Then, one day, researching stars to help your little sister with a project, you stumble across the star betelgeuse.... It sounded so familiar. It looked familiar, the spelling. Then you remembered. It was the TRUE spelling of Beetlejuices name, though he preferred to spell it as Beetlejuice to avoid confusion, it was his true name.

You finally remembered it... You remembered your lovers name. So you quickly said it three times to summon him back into your life (and technically, into your room). And soon. Your (groggy) lover, it was two am, after two years, was in front of you again

"Yeah yeah. Whaddya want." His eyes were closed, as he was rubbing them. He hasn't realized it was you yet