Aww, that's so hard
No reason you can't do half days to start with and give him a chance to settle in.
Two things I'd suggest. Before starting DS at daycare I went with him for a few hours in the morning 1-2 a week to give him a chance to get used to it with me nearby.
The other thing is if you're leaving, leave right away. It's hard (worse for you even) but better for them in the long run. You say goodbye and go and they learn that it's ok, you will come back.
All the best - it's good that he's keen.