Well, first article regarding to lovelife and I'm going to start with an old greek "joke", which is pretty relevant:

boy: i want us to break up
girl: ...
boy: but...we can be friends, right?
girl: my dog died but i think i'll keep it anyways, how does this sound to you?
The boy did't reply. GUESS WHY!

I, personally, can't kiss on the cheek a person that I was tongue-kissing before. I really don't get it. Like, I already have friends, better than the asshole that made my life difficult, even for a short period of time.
Furthermore, a friend is someone you can trust about anything, including your lovelife. So here comes the question: Can you talk conveniently to your ex about your current lovelife? Most likely, no. Cause if you still fall for your ex, then why would you talk to them about somebody else? And if you have got over them after a lil heartbreak, how could you trust them with such personal stuff?
On the other hand, every "rule" has its exceptions: If after the breakup, there were no heartbreaks, you may feel like friendship is an option, so go on! I've felt so once and he really is a friend of mine since 2014. But for me it's an exception, not the rule.
Last but not least, don't forget that having typical relations with an ex is not only polite, but also a humanity and maturity trait!

love, couple, and boy image

That's all I had to express about friendships with exes; hope you enjoyed! At this point, I have to add that everything I've stated above is seen from my personal point of view and it's fully respectable if yours is different!