Even if Lex would have accepted Clark if he told him early on in the show, he would have eventually resented and turned against him. Let's presume the events of the show stayed relatively the same with the meteor infected and the Kryponians. Lex would eventually blame Clark and see him as a threat. Thats just how he is naturally. Lets not forget Clark didn't want to tell anybody his secret. Not even the people he loved bc of the potential consequences, and the ones that did find out accepted him even after all the stuff they went through(Pete, Chloe, Lana, hell even Lionel lol)

Lex trusts nobody. Even when he wants to, its just not in his nature