I read this a few days ago, and it's still stuck with me. Star's comment did too because I remember watching "Bridge to Terabithia" as a child, something so moving and powerful about loss and imagination.
The emotion in this, the depth in such few lines. I liked how you took it further, as I've heard so many times that the grass is greener on the other side, that we can compare and compare yet we need to be reminded that we have it pretty good, that it may not appear everyone else has it better than us. You took that proverb and made such a connection with it. How I perceived it as giving someone permission, helping them, to move on from you. Perhaps thinking that this will give them a better future, yet you've come to regret it. It reminds me of a few other films (can't think of the titles at this moment) where the person walks away, almost as a sacrifice, saying "someday you'll understand" because it may give the other person more time to grow into who they are instead of jumping into love.
My only other comment is that in the fourth line, I don't think "grassed over" worked that well, just my opinion though! Since you already mentioned "grass" and there is that theme, I wasn't the biggest fan.
I love love the story you wrote here, although it is emotionally sad, you penned it well. The metaphors are expertly crafted and relatable to a lot of people and you owned your emotions. Anyway about the poem itself.
There is a bit of hope at the beginning and it is you helping this person cross into happiness, and you are that happiness and are there for them no matter what happens. I love the wording and the way you build up to the plot point as well. Then
everything falls apart. It seems once again the beginning is a memory of happier times and the middle of the poem brings us as the readers back to reality. Almost like a flash back or an attack.
Back to reality you are weeping because the memories are too much to bare. This person caused you pain.
The ending three lines hit you hard and you truly feel the sadness in them. This person used you to get what they wanted and they stepped on you. You being the grass. You being the other side.