Well this has been going on a lot longer than 5 months hasn't it salisbury/jibjab? No you are not in love, but you are pining.
When a relationship ends (or you lose a loved on) it is always difficult moving on, and there should be no harm in thinking about the lost love - we all do it occassionally - even us married ones. But you need to put it all in perspective and as you have said, you can see now that she wasn't really right for you and even if she hadn't ended it - would things really be right and stay right between you?
As 4gotten has said, you do need to move on and this takes time. There will be an element of comparing with a few girls in the beginning but eventually you will find someone who ticks alll the boxes that your ex didn't and in time you will forget to remember her each day as you might well have someone else to think about and focus your attention on.