Slap that spurt right out of him!
This is an example of a cuckold where I could not have his wife use his nuts to moderate his excitement.
Typically when I’m directing some edging play with a couple, I will have her back him off from his excitement by flicking a testicle or giving them an open-handed slap, but for some, that testicle abuse just pushes them over the edge. For them, I’ll have to use ice packs or show him pictures of his mother in law :)~ .
For easily excitable cuckolds, draining them once manually can sometimes be useful before allowing him to watch his wife’s coupling with her lover.
One final note: look at the power of that spurt – guaranteed that it landed on his face!