The best thing would be to write down events from day to day.
Day 2
On a dull, grayish morning in Our Town, you trot down the street. The townsponies glance at you and then look away pretending not to have seen. You don't think that their denial will help them with anything, but you do not blame them; unflinching acceptance of and despair at literally everything is one aspect of your special talent, and you can't expect it of everyone. That is what "special" means.
When you get to the end of the street you knock on the door, and wait for Starlight to answer. She takes a few moments longer than you would expect. Maybe she is making you wait as a power play. It will not work; knowing that nothing can make life worse is part of your special talent.
"Morning Starlight," you say, "My cutie mark is back." You don't meet her eyes.
"Hi Sisihooves WAHT‽" She interrobangs.
So you turn to show your flank and then look back at it. You see your cutie mark: a pony rolling a boulder up a hill.
"Are you sure you removed it properly?"
Day 10
When you think about it, it is strange that none of the the other townsponies share your problem. The ponies of Our Town do not tell cutie mark stories, but literally every other pony you have ever met does, and one fact is clear: even foals can do it. It is not like you got generally less good at things as you grew up - why did they? why isn't anyone else in Our Town constantly manifesting marks?
Day 25
Starlight doesn't ask questions about the cutie marks she removes, and you don't offer the information but you know that a pony rolling a boulder up a hill means a lot of things. Physical labour, obviously. The inclined plane. The punishment of the old king who escaped Tartarus (he bound Death in is own chains, and fled). Finding meaning in the endless futile struggle that is called "living". The meaning you find in this ritual is this: the twitch over Starlight's left eye: you think it is some sort of code.
Day 47
You are the boulder. You feel the great wizard strain to push you to the markless hilltop. You roll down again. You are the boulder. You are dumb unyielding mass, seeking the place of minimum potential. Your mass calls to the mass of the earth and so you roll to the bottom. You are the boulder.
Day 135
The day dawns late and damp, and you trot across town to Starlight's house. The townsponies are used to this by now, and greet you in a friendly enough way, although the offer of muffins could be interpreted as a threat now that you know what they taste like.
Its return is not a surprise. It is, after all, a mark for endless labour. It would hardly be that which it is if it did not come back. When you get to the end of the street, you knock on the door, and wait for Starlight to answer. She always takes just a few moments longer than she should; enough to make it obvious that she is hiding something and has no talent for doing so.
"Morning Starlight," you say, "My cutie mark is back."
Day 365
You have done this every day for the last year, so you stop off on your way across town to buy some terrible baked goods and a substandard candle. You attach them to each other and set one of the them on fire before you knock at the door.
"Happy cutie mark removalversity, Starlight," you say, "It is a new celebration that I invented, for ponies that have spent a year removing cutie marks together."
You are not a great judge of expressions but you think that maybe she looks tired. You try to cheer her up.
"Isn't it wonderful how constantly removing ponys' cutie marks has brought us all together?"
You are explaining yourself badly; you always do, but there are somethings you don't even know how to think: I was lonely. I don't know how to be friends. I'm glad I have some reason, every day, to talk to someone. I wouldn't know what to do if this stopped.
Day 1235
You find that Starlight has been ran out of town. Now you'll never find out if her monomania is stronger than your commitment to the role.
CODA: Day 1537
It is a bright sunny day in Ponyville and you trot down the path to the Stronghold of Amicability and knock on the crystal door.
"Morning Starlight," you say, "My cutie mark is back."