"You read and I sleep."
Translation:Jij leest en ik slaap.
Actually, there are several cases where "je" is valid as replacement of "jullie" (for example, possessive pronouns), but "jij" applies only to the singular, without exceptions.
@oximan1 - since it's been 3 years since you asked your question, I'm sure it's clear to you by now, but I wanted to add this in the comments here for future beginners. ;-)