What season and what episode was it where Chloe(posessed by someone else) made a pass at Lana?

Wasn't that in season 4, episode 8, called "Spell"?

Either season 4 'Spell' or season 3 'Delete'.

I've got one:

I stopped watching the show halfway through...season 4 I think? The season with Jensen Ackles. I started up again with the next season.

Was there a specific event that "ended" Clark and Lex's friendship? I'm racking my brain and cannot think of anything beyond the usual "Lex trying to find out Clark's secret" but I'm wondering if I missed something big.

I don't think there was a specific event.

During Season 5, Clark got some insight into Lex's nefarious activities courtesy of Milton Fine (aka Brainiac)
and then Pa Kent and Lex faced off in the senate race

Along the way Clark began to see the ruthless, murdering, megalomaniacal side of good ole Lex

I thought clark broke it off with lex for good when it became apparent that he was with lana which seemed to happen in season 5.

Actually Lex broke it off. It was a long drawn out event about their relationship going sour, but the final straw(not sure which episode) Lex ended the friendship and it happened in a greenhouse. I remember it well because Clark went there to investigate something and Lex just happened to be there. A big moment.

Lex told Clark his days of intruding on his property are over told him to never show up unannounced again.

Doesn't it all tie into those artifact pieces everyone is collecting in S4?

I saw the season with Milton Fine (season 5? Are we in season 6 now?), I just don't remember a specfic moment where things went south between them, at least more so than they have in the past. A moment where Clark went from defending Lex to hating him.

Sounds like there wasn't really one.

Actually I think DVD-4-life is talking about Season 2 an espisode called Visage where a character called Tina Grier transforms into Chloe because she's trying to get close to Lana. Of course they never really flat out say shes a Lesbian but when we catch her smelling lana's underwear/lingerie I think we can pretty much come to our own conclusions lol She then goes up to Lana (who's wet and in a towel) as Chloe and touches her back while checking her out.