The most sexually arousing moment for a cuck is when you are undressed with your wife and another man.

 when His penis is significantly larger than you it turns you on 

when he is stronger than you and could easily beat you up it turns you on

when your wife tells him he is bigger and stronger than you it turns you on

when he penetrates your wife bare the faces she makes enjoying his superiority in every sense turns you on

when you go limp while he still goes it turns you on

when he cums inside her and doesn't withdraw until every drop has been drained in your wifes married pussy it turns you on

thevsight of his post sex dick withdrawing and covered in his juices snd hers turns you on

licking out your wife after he is done and eating all his cum turns you on

him kissing her passionately good by turns you on

your wife refusing to let you fuck her after he has gone and not allowing you to cum turns you on

the cold shower you need to take to compensate winds you down