what happened to my cherry tree? and how to help him?

Ants farming aphids on the ends of your cherry branches. I’m dealing with it too. Can try neem oil but it’s doing nothing for me. I try to avoid serious pesticides but I had some permithrin laying around so sprayed the leaves to take care of the ants and aphids. I have dogs so have to be very careful. Also don’t want to harm bees.

You can try a systemic aphid killer. Start it early next year to prevent this.