Try to open the center up. Remove all branches going inward. Aphids are so easy to control, and the ants will go away if no aphids. Just spray insecticidal soap every 7 days. You could even just hose them off.
Use All Seasons oil too, if you want to make sure. Stick to the soap when hot. The ants want the aphid poo, not the cherries.
Nice looking tree, and so easy to solve the problem.
Trim all branches down, as too many cherries produce at the end of branches, and not enough leaf to feed them, so cut back all limbs. See the buds at the end of the branches? See how say 6 inches to 2 feet in, they are farther apart? Get rid of the cluster of buds at the end of the branches. Your cherries will be bigger, and better tasting if you remove about 1/3 of the branch. About where the buds spread out more. You have some big branches in the center, I would remove. Maybe not all at once, but one a season to open the center up like a bowl.
You want to form a bowl, open in the middle so light get's in, and air circulates.
Go to utube and search how to prune cherry for a more detailed description of what you need to do. Look at the MSU and Oregon videos.
Pruning advice I gave is for a sweet cherry, if it's a tart check the videos for proper pruning of tart cherries.

Thank you so much Drew51 for your comprehensive response. I have taken a look at your instructions while looking at my tree and it seems to be a wonderful idea you have. I will begin the pruning process shortly and post a photo once the first stage is complete.

Thank you very much again. I really appreciate your help and consideration.
Cheers