He erased Sakura and Yue's memories, once each mind you....
Secondly he schemed for Sakura's well-being, he knew if he told Sakura eveything, she wouldn't be as determined to stop him and transform the cards. Also, Sakura had to transform them with a purpose. So, Eriol provided a purpose, and that was too try and stop him. He also knew that if the cards weren't transformed, they would 'die', he also knew that the cards were really special to Sakura, and he knew if the cards weren't there anymore, Sakura would be sad. He wanted to help her, his intentions were good, he did the right thing, he did everything any one would do.
I think Eriol is very kind, and wise. He thinks about the bigger picture, he doesn't scheme, he merely tries to use methods that are unseen to people so there are better results. He cares about Sakura and her happiness, which he shows plenty of times.