How do you go from being intimate to becoming buddies?
In my personal case, it is because my ex has a lot of issues that he's never dealt with. In his words to his mother "I treated Heaven poorly."
He's the kind of person that once you're in his core, he can't handle it and pushes you out. It took me years to realize that while he cared about me, he had a lot of issues with this and that he did not care for me the way I needed him to. And I also realized he never would be able to.
So I felt it would be better to be friends than to be in a marital relationship where he was unable to come to the table. I tried to help him over the years; begged him to get help but that ultimately must come from the person themselves. He did eventually go for a few general counselling sessions which netted out that he needed specialized help. He never went.
Thanks to my JW upbringing, I have developed a few 'opposite' modus operandi in my life. I do not wish to discard people just because things get tough. I develop my own methods for coping but I don't like discarding people and I avoid it as much as I can. I fight every day the judgmental attitudes instilled in me by my parents. None of us is perfect and I try to remember that daily. So me and my ex are 'friends'. There are many issues between us that prevents me ever wanting to be intimate with him again. Choose carefully the words and actions you take with those you care deeply for as these can make and break relationships.