It is definitely not painful when… you were obsessed with something and asked her/him to join, but she/he refused because she/he called “this” as an obsessive thing and she/he didn’t want to be involved, and after some time she/he started obsessing the same thing and it seems to be pretty much fun to her/him.
And you never know, what was the reason of rejecting your stuff and then returning to it after breaking up with you.
I am making it clear. This is not painful, this is kinda offensive.
P.S. I wanted to say “I wish your obsessions got so big that it makes you lie, cry and die” but that would be too cruel of me, wouldn’t it?