The story goes sorta like this 1. Blair sees Eva returning her watch at Cartier, thinks she's up to no good, goes to Chuck but Eva actually was getting money to pay for Chuck's valet's mom's freaking house, Chuck and Eva kiss in front of Blair WHICH IS GROSS
2. Blair is determined to dig up dirt on Eva, finds out through Dan and Serena that Eva's a prostitute
3. Dan tells Nate that Eva is a prostitute, Nate tells Chuck, Chuck pretends he knew but he didn't, forgives Eva for lying by omission
4. Blair goes to Chuck's gala and tells him that Eva's a prostitute, Chuck knows and doesn't care, she's aghast and tells him not to repeat his mistake with his mother, Chuck tells her she's just jealous that Eva changed him when Blair couldn't
5. Chuck dedicated a 5 million dollar charity in Eva's name for whatever she wants it to go to, this pisses Blair off so she plants the passport and shows Chuck it, Chuck breaks up with Eva but then he finds out that Blair planted it, he tries to apologize to Eva but she says she's leaving
6. Chuck goes to Blair's house and asks if she hates him or if there's a possibility she still loves him, she wants to tell him she loves him but she can't so she says "how could I ever love you after what you did?", he's all YOU HAVE BROUGHT BACK THE WORST SIDE OF MYSELF, THIS MEANS WAR, NO LIMITS
7. Blair goes to Serena crying and says she just can't forgive him, the script says Serena realizes Blair still loves him
SO! Yes, she does sabotage him. But when she tells Chuck that Eva is a prostitute, that's the truth. There's no sabotage there yet. She is honestly looking out for him at that moment and when she warns him that this could be the same exact thing that happened with his mother, he insults her. And, as an aside, when he does find the passport (which she did plant, but which he doesn't know yet), he says to her "how could I have ever believed that someone who was actually good would love me?" So even when he thinks she's telling the truth, HE'S STILL INSULTING HER.
Source: comagirl
Here is some info on Episode 4.04
Blair comes off as not being able to forgive Chuck, but also not being able to let go. Her motives are actually good, though. She has reason to believe Eva is bad. Turns out, Chuck DIDN'T know Eva was a prostitute. Dan, Serena, and Blair discover that. Blair's scheming is justified in the end, because she tells Chuck it felt like the situation with his mother again, where he was being taken.
Chuck, however, is ALL ABOUT EVA. He is now talking to his valet, donating to charities. He sets up a $5 million charity in Eva's name and gives a speech about her at a fundraiser talking about how amazing! she is (oh, this is in front of Blair). He tells Blair that she's just mad that Eva changed him and she didn't...yup, you read that right.
Then, after Blair plants the passport (she does it because she finds out Chuck was lying to her when he said Eva had already told him about her prostitution - she finds out he didn't actually know, and legit thinks Eva is playing him), Chuck breaks it off with Eva. When he finds out it was Blair, he rushes to Eva, apologizes, once again tells her how good she is. Eva says there's a "connection" between him and Blair and he doesn't deny it, but proposes them running back to France. Bottom line, he's hanging onto her because she makes him annoying, er...good.
After Eva leaves, he goes over to see Blair. Asks her why she did it. She tells him she was trying to protect him. He asks (the scripts says "hopefully") if she did it because she loves him. The script dictates that Blair pauses, because of course she loves him, but she says, "How could I love you after what you did." He then seethes and declares "war" against her, "the likes of which this town has never seen." Blair ends the episode crying with Serena.
Yup, Chuck Bass has actually managed to out douche himself. Do we think EW is leaving the show? Honestly, they're making him the most ridiculous ass ever.
Source: gossipgirl_anon