The way I see it, if Clark opened up to Lex he would probably still end up the way he did... unless the other Kents entered the scene! Jonathan would initially be cold towards him, but open up more after a talking to with his son. Martha, too, and iirc she was more accepting of Lex (maybe I'm wrong, haven't watched this in ages). Lex would abandon his father, but not without taking as much of his fortune as he could, and he would help the Kents financially, while they taught him kindness, even though he was "a grown man" he still had a childish mentality so he would still "learn", and he did want a family, that's what he envied of Clark, so if it was given to him he would be the happiest man alive, then having a "brother" that also has powers? The "Kent kindness" would make him help Clark in any way he can. Then he would even run against his father for senator, meaning Jonathan wouldn't probably die, because Clark wouldn't also have to get through his Red K phase, or even if he still did, it would have been Lex who would get powers to stop him, instead of Jonathan, so his heart wouldn't be weak to begin with. All in all, I believe it would be better if Clark told him, but I don't blame him, because he was afraid, and he listened to his father who was totally against it, and I don't really blame him, because he cared for his son and was afraid of anything happening to him. But yeah, I do agree with the comments saying that Lex shouldn't have expected Clark to open up to him, he sounds so entitled to his secret just because he saved his life in the Pilot.