First, don't worry about the red bumps on the leaf stems; these are nectaries and they are meant to be there. You may notice ants visiting them because the nectar they produce is meant to attract some beneficial insects as part of the tree's defence against other insect invaders. They are not what is causing the problem with the leaves.Second, your tree is not currently dying!
On the subject of the new leaves, I can't quite tell if there are aphids present from the photograph - check under the leaves to see if there's any there, because they look as if aphids might be an issue. Aphids can be black, white green and sometimes brownish and they look like tiny flies -you may need a magnifying glass to inspect thoroughly. Ants on the plant (other than visiting the nectaries) also may indicate an aphid infestation, because the ants harvest the honeydew the aphids produce.
Otherwise, the weather has been hot for the time of year (especially here in London) as well as very dry; your tree will need at least a couple of litres of water poured round the base about every 5 days until the weather breaks and rain returns. Ongoing be sure to keep it watered during dry spells - young trees need to be kept supplied with water during spring and summer for the first two years,until they have put out a good root system to seek out their own. If you have not yet given the tree any balanced fertiliser, do so now - something like Growmore granules sprinkled round the base and very lightly raked in will do the job.
Information on cherry tree problems here https://www.gardenfocused.co.uk/fruitarticles/cherry/pest-disease.php