This question is quite well answered in this book..
http://www.amazon.co.uk/Men-Mars-Wom.../dp/0007152590
Having been in two long term relationships (both 10+ years) I kind have figured out quite a lot about how we interact over time.
One thing is for sure we individually change and think reading this book will give you an insight into a guys mind.
Generally guys are pretty simple - I have found the females (apart from last gf) to be very chaotic with moods resembling a graph of the FTSE 100 over the last 5 years
Anyway not wanting to say too much more cos I like sitting on the fence!!
Tone