Ah Ying worked for Bruce until Lee's death. Their friendship was a well-known fact. They collaborated very well together, they both had studied Wing Chun as a fighting style and were serious in their work. Of course at the beginning they had their manly contests to size up each others' limits. Ching Ying anyway was a very proud man and not easily admitted someone else's knowledge and quality unless he had already proved. The story is that he didn't think that Bruce was as strong as it was rumored. So in a hotel room, he challenged Lee...They put a pillow over Ching's chest and stomach...And Bruce kicked and hit....The pillow and Ying were sent flying across the room, nearly through the window. Sure their friendship, as it is proper between men, went on smoothly. Ching Ying learnt Lee's border.
Ah Ying was still very young, and as I mentioned earlier, he was not as easy person to handle, still had his games to learn from. At one point, filming was suspended on The Big Boss, because Bruce had to bail Ching Ying from the jail as he had been arrested for fighting. This was not the last time he had trouble with the police. He was stubborn, driven, and when he got something into his head it was impossible to divert him. 
This headstrong, self-willed young man was Bruce's favorite. Not many people know this, but Lee was a very shy guy and kept a lot of things to himself. But he loved making people think. Lee challenged the beliefs of many philosophers and intellectuals. He loved a good conversation and Ying was the proper person for him. He could use his brain, even he wasn't as educated as Bruce was, had a clear mind, he was bright and wise despite his young age.
So Bruce rehired him as his personal assistant and co-action director when filming for Fist Of Fury began. During Enter the Dragon Lee made a special request to Raymond Chow to get him back from Korea to be his action director. In this one Ching Ying played the stunt double for Shih Kuen who portrayed the villain, Han. Their working relationship and friendship continued through all of Lee's films until his sudden death.
Ah Ying was incredibly saddened by his loss, as he had a great deal of respect for Lee. This respect of Ying's was a topic of conversations throughout his life between friends and co-stars. If he didn't respect you, he had very little time for you. He would even turn his back on you, if he felt there's nothing in common to talk about. Maybe he felt beforehand that he will not have much time in this world for an unworthy chit-chat.
Lee died during filming Game Of Death. There are rumors that he and Ching Ying completed some fighting scenes, made huge changes and there are much more footage that was actually used in the final version. Kim Tai Jung says he saw a 90 minutes long, continuous film back in 1975 with Ching Ying. Lam stated these were all filmed by Bruce. Ah Ying can be seen as a karate fighter in outside picture stills against Bruce Lee. They even talk about notes Lee gave Lam right before he died. This is a mysterious game. They are both dead, and the tape is lying somewhere in an attic at the Golden Harvest Studios. One day we might see the truth.
After Lee's death a new era started for Ching Ying.