If you have the ability to be friends with an ex you can. It is usually the ex who can't process or be friends with you and ultimately (even if indicating they want to be friends badly) most definitely don't put in any effort into any form of friendship most of the time.
NB, you being male. ex being female.
As for if it works. It can definitely, but it takes a level of maturity from both parties which I think is lacking in today's society.
The [-]heart[/-] mind/penis/vagina has the ability to complicate everything.
Fixed that for you

Truly being in love with each other has 0 complications. Taking from a friendship to full fledged relationship/partnership back to friendship (when a breakup is mutual etc).
What complicates things are your own insecurities and past which you bring forward into a new relationship most of the time (both of you). It takes more effort to work at something (and I mean truly work at something with open and honest communication) than it is to pick a fight/fight over things that doesn't matter. And it all starts with the first lie: "No, I will never lie to you and will always be honest with you... even if it hurts your feelings". Show me someone who meant that and I'll show you my lucky charms and pot of gold (yes, I'm a leprechaun)
That... and the inability to CALM THE **** DOWN and discuss things like adults. Women love the sarcastic/throwing past grievances in your face route and you defend yourself with the same hurtful **** in the end (or other way around) instead of approaching an issue like 2 sane adults with the common purpose to resolve and grow with each other into one.
Anyway, nuff about my ramblings... how big were her tits?
NO I am NOT drunk... I'm not sober either...