Being a friend with your ex

He knew what they had was over, he knew she is going to be someone else's but never did he expect it would be so soon. They both were happy post the break up with their own lives, they were friends, they chat and call each other, she still cares about him talks about what's happening and suggests a lot of ideas just as if she is still his girlfriend. She was meeting a potential match and moving on, he was moving on looking to date someone new, but feels the emptiness every time he has something to share but has no-one, feels sucked down in to hollowness every time something he saw in front of him reminds of the small and cute gestures she did when they were together. He imagined maybe sometimes she goes through what he goes through but then looks at social media post that "she is happily taken" about the engagement. He thinks is break up easy, well she moved on looks like she is happy he tries to move. He thought it was not a bad break up and they are friends, everything is well and they have their lives going on but only when he saw the post realized he still didn't get through the break up but just trying to. He is looking for someone to come into his life as well but then every time he has a conversation with that someone he realizes its not her, they don't carry the same magic that he and she had between them. He know he cannot do anything to work it out, he know break up is tough, he know he has to move on, but never did he know that being a friend to your ex is strenuous and grueling.