Hello,
we had the same topic a few days ago at the forum.
If he is inactiv, he will remove automatic after some days from your friend list.
Don't send him friendly boosters any longer.
That´s the way how it worked on my account.
I also have seen now,
the red cross to delete someone of your friendlist is just there if you added the friend directly in top eleven!
The Facebook-Friends have no red cross in the upper right corner of there profile-image!
So, if he is still in your Facebook-Friendlist, you can try to delete him there.
If he is no longer listed on your Facebook-Friendlist please have the patience for a few days,
don't send him daily-boosters and if this not helps write again here.
Alternativ Options:
-Contact Facebook Support to delete him from your Friendlist there.
That's what i think about
Best regards