if he loses all of his short term memory, he will forget that he ever saw clark stop that car. their friendship won't end yet. it's not time.
and i don't think lana and lex will be together. they've presented her as what... a 16 or 17 year old and he is much older. i can't imagine that. in my eyes, though clark and lex are friends, i still see lex as an older guy/older brother - so i see no connection between him and lana.