OSU has a good couple of bulletins out regarding the stressful period of time it is for cherry trees of 4 years age or less. Consider yourself in that same period of stress because of the way the seller short changed you. Which is the possibility the tree is crying for being chopped at so completely during rainy event with high disease outside, or if it were grown in a greenhouse and not threatened by disease yet then it knows feeder roots are missing and water supply is at a minimum. Both these scenarios are kind of covered in the background of the bulletins from OSU in my eyes when you know the external links to other studies regarding disease and sweet cherry stress. Sour cherry types are more forgiving and will take more of a short supply of the root mass than sweet cherry so the OSU one dedicates the bulletin to sweet cherry problems than problems with sour cherry. 

In the fall of 2021 while I was transplanting clonal cherry clones that were coming from mature sections of roots from the much bigger mother tree were also short of roots. Maybe it was the last part of 2022, but I watched the tallest one with the smallest root mass continue to struggle for one half of the next year or one and a half years before resuming to normality. This was wild pin cherry in interior Alaska though and still I tried to keep watering around it as a way to keep humidity up. Fortunately I had enough flexibility in the stem to bend it down into tall grasses to prevent sun damage too. This last summer it was well enough to grow normal looking leaves and it had a few cherries.

So after you read the warnings from OSU then you also might think of doing almost the same thing as I. So if you can't create shade, low wind, and humidity conserving methods then unfortunately you might be thinking of potting it up and laying it in tall grass for the summer if it doesn't rain too much there (where you live?). 

Most of the time I am local SW Washington. I have seen stress on trees and especially sweet cherry grafted with dwarfing rootstocks for the first several years of time when grown fully exposed. My 'blackgold' cherry on gisela-5 was in excellent shape from the nursery and taken care of in soils that were acceptable. I actually had to save it from dying by placing rain shelters over the branches for at least two years a few years ago. All the branches that rain got to died off, but it was worth the effort because of the branches that self pollinate do well for me to this day.

So I think it's easier for you to keep yours mobile for at least a year so it can be put under eaves for the winter season or two. You would need 20 gallon pots for a multi-grafted sweet cherry like yours to get enough root mass and enough soil so that watering in the absence of rain won't demand you doing this (in dormancy) too often.

If your local I can expend scions of other cultivars. If you have skills and knife experience you can just cut down to the ground and build a small and new fake greenhouse environment for a year and a half. But you can get 'blackgold' sweet cherry, and a high quality yellow sweet cherry. I still graft this time in the year and as long as bark slips it's okay.