Y answered that it wasn't a matter of E "making up" for it, but that he just wants E to be proactive in taking his feelings into consideration.
That could mean...
"Do not ding me intentionally. But don't ding me THOUGHTLESSLY either. Consider me and my needs when you do things. You are not a footloose single. You are a trio man -- a "V" arm guy. What you do affects not just the shared sweetie hinge but me in my life too. "
Now he has his own work in getting comfortable with seeing displays of affection between you. He too is a trio man as a "V" arm guy and deal with the realities of the configuration.
But you all could talk together about the pace of that. Maybe the "for now" thing is "do what you wish behind closed doors but in "common areas" of the house try to be more chaste for the next month" to give him a chance to put a toe in the water and not be all ACK! about it.
Getting used to the "new normal" takes some transition.
I hadn't considered asking together with E before because I was afraid it would be perceived as double-teaming, but since you have phrased it in terms of goodwill, I can see why that would be so important
Doesn't have to be both asking at the same time.
Could be you bring it up to him one day. E brings it up to him another (but still reasonably close together) day. Or a joint written letter so he has time to digest before responding so he doesn't feel "put on the spot."
Easiest is to just ASK him how he prefers the
(You + E) ----> Him
tier of things goes. How he prefers the couple to approach him so he feels emotionally safe enough to give E opportunity to demonstrate better. Because it's DH who has to risk giving the chance
to find out E has changed and improved. He's risking the ding.
If he has no goodwill for E, he's not going to feel excited about taking the risk to see that yes,
it is true! DH can now do that and come out UN-DINGED by him. And so begin to build trust in E with DH's emotional safety.