I don't think not texting happy birthday to his ExW makes him a mean guy. Imo stopping those actions might help him start letting go and moving on.

Me:39 Ex-W:37
M:7 T: 9
S:6 D:3
BD/IHS/Confirm EA/PA: Feb '20
OM1 affair ends: May '20
W/OM2 & moves out: June-July '20
W files for D: Jul20
OM2 confirmed: 9/2020
Divorced: May '21