ما يَصْعُبُ تحمُّله يحلو تَذكُّره what koko said is also true but he wrote it as if he was talking to specific persone , I mean if you wrote (what was hard for you to bear it will be sweet for you to remember ) what Koko wrote would be more suitable for that.

ما كان من الصعب أن تتحمله جميل ان تتذكره

ما كان صعب التحمل كان حلو التذكر َ