Maybe I'm a hard cold bastard, but I always use that "I love you" line on newer GFs who aren't yet satisfied with being merely a fuck buddy. Once they know their place, I never use it.
The first time I honestly told a girl that "I love you", she responded with "You're a jerk." I quickly learned my lesson.
To my best long-term GFs, we have pet names and silly phrases we exchange like ducks that bob heads. Long-term pair-bonding is great. I miss them terribly when I'm away on business. But I'll never fool myself into believing that missing a friend is the same as falling in love. It's not. Not by a longshot.