He didn't care
Pretend.
He didn't care about the fact that he had to pretend to not have the feelings that he had for Sasuke a secret, because Sasuke had asked him to hide them, and he would do anything for him.
He didn't care that he had the slight feeling that Sasuke would purposely try to put him down I front of others. He would just surmise that to being how they were used to being seen
He pretended that he didn't care when he heard the engagement of Sasuke. He knew that it was only because Sasuke needed to produce an heir.
He pretended not to care when Sasuke told him that he didn't need him anymore, but would stop by occasionally in the dark for a quick fix when he couldn't get any from his wife.
He pretended to not notice that he was dying inside. Slowly and painfully.
He was just so good at pretending that it had become the norm until he couldn't tell the fake form the real. Not that real mattered anymore, because now he didn't care.