Perhaps too late - I see the precious post was 2 weeks ago...
But don't 'water it mightily'. Trees stressed by drought can recover if watered carefully. But they can be killed if given too much water too quickly.
An example: In the southeast of England in 1976, great numbers of mature beech trees suffered badly in the severest drought in decades. It was followed by heavy rains, and it appears that it was the excessive water that finished them off.
To confirm it is F. ornus, since you have seed, you should have seen fluffy-tassley white flowers in spring.
That amount of suckering makes me suspect damage to the trunk, possibly low-down.
Are there signs of damage from strimmer/brushscutter?, other obvious signs of damage, or less obvious damage such as borings of ash bark beetle (Hylesinus varius) under flakes of bark? [https://www.forestryimages.org/browse/detail.cfm?imgnum=2105017]
Mike