The leaves on my cherry tree have developed dark, round spots which then fall out, leaving the foliage full of holes, how can I prevent this happening?

The damage is caused by the  fungus stigmma carpophila., and prevention is easier than cure.

It tends to affect weak sickly trees, so ensure you feed and watering as necessary.

An occasional foliar feed will also help.

Spray affected trees with a bacterial canker control at leaf fall.

I would like to grow a dessert cherry but I am told that I need two varieties for pollination

I have only space for one tree, are there any self-fertile varieties?

At one time all sweet cherries needed another variety as a pollinator, but in recent years a number of new self-fertile varieties have appeared, check with a specialist grower for varieties.