Chibi Halo
You have to take into consideration what's going on around them that could be influencing what's happening in their relationships. Asami's world is crumbling around her. Her father's in prison, she can't keep the family business thriving on her own, and quite possibly the first guy she had feelings for broke up with her. Out of desperation to gain some kind of control in her life Asami turned to a successful yet at the same time questionable businessman to save her business. However, that turned out to be more bad than good. The moment she hooked up with Varrick her company was the target of thieves who nearly spelled the end of her family's company.
The moment she gets some help from Mako I do think Asami began to feel some level of control in her life. She started to feel as though there was something in her life she could control again. She's desperate for the familiar and comfortable. So when she gives away control of her family's business Asami turns to Mako to bring back the familiar. Because there's still some residual feelings between the pair and Mako is technically single having broken up with Korra and Asami doesn't have anyone in her life it was easy for him to reciprocate those feelings even for a brief moment or two.
The thing you have to remember is that the moment Varrick entered into their lives Bolin and Asami became very oblivious to everything going on around them. Why would they have reason to question the true motives of a man who "saved" a business and made someone the very first movers star?
At this point, I'm mostly pissed off at the fact that Mako can just keep switching between these two girls whenever he pleases. He isn't held accountable for playing with their feelings and emotions, and his views on ending relationships DISGUST me. Did you HEAR his so-called "advice" to Bolin when it came to him wanting to break up with Eska? "It's like ripping off a blood-sucking leech?"
Really?
Well aren't YOU just so charming?
stare
As for Asami, I agree that you definitely make some valid points. But my main problem with her is that she's too perfect. Honestly, she puts me in mind of a Mary Sue, and I don't really feel that she offers anything to the show other than supplying a love triangle (and a really irritating one, at that). I think I would've liked her better if she would've turned evil and joined her father and the equalists. Would've given her some more depth and character growth.
But all I see when I look at her is just a rich pretty girl with an electric glove.