Most Helpful Guy
Sometimes people leave their facebook open and hence you see him online. Unless he's commenting or posting then it shouldn't be a big deal. In addition, sometimes everyone just need a break from talking or something, specially if all the other person does is nag and complain about stuff, and/or talk about stuff you don't really care too much about; everyone has those days
Most Helpful Girl
By online do you mean you can see him with the green circle next to his name or online as in posting thing?