He was poisoned when he was still inside his mother's belly. That was the reason why his body was weak since he was young.
Although he did not die from the poison, the poison was slowly and gradually damaging his body. Hence, he did not know how long more he had to live.
Grandmaster Qian Kun had the same opinion too.
If he was doing fine, he would be just like any healthy person. He would only appear weak.
If his body's health deteriorated, he would be dead any second even if he was fine before.
That was also the reason why he did not get married.
He was afraid that he would ruin an innocent girl's happiness.
"Young lady." Mu Qingyin did not want to dwell on the past. He laughed. "I've never met you before. But, I trust my sister-in-law. Master's birthday is around the corner. If you want to come, we will welcome you with open arms. If you're unwilling to meet somebody, it's fine if you don't want to come and join us."