Yes I understand!
DH and I have known each other for 21 years, together for 11. BF and I have known each other for 16 years as best friends.
I can't imagine someone just "plopping in" and thinking that they could begin to replace that much TIME.
The more time you spend together the more you grow together and become more.... what is the word??? I think of it like a braid.. you are just all tied into the fabric of each other.
That takes time together, not just sudden passion.
It's funny cause when you all write-I dont' really think "huh which one is this" since your pic has both faces I just sort of assume I'm talking to both of you as if you were sitting together on my sofa!