Welcome to the forum.
Was he being aggressive this time. I know you do not want to chance him hurting the chicks or the hen, but right now he has a job he is supposed to be doing and he can't. This is probably the source of his stress.
If you are going to keep him separated, you should move him completely away from the hen.
You should probably take some measures to make sure your hen does not have another clutch. It takes both parents to raise the babies. This is going to make it more difficult on the hen.
Good luck.
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Barbara