Yeah i'd say it's common.
I have not long broke up with mine, and although i care for her i'm not desperately trying to get back with her, i hope it happens in the future..but for now it's a no no.
I want her to be happy, even if it's not with me...but at the same time it would kill me if she was with somebody else...it's not having her that scares me, it's her being with other people.
So i'd say it's normal, don't worry.
Although 18 months is a long time, not saying your feelings should have gone...but, you need to take your mind off it!