There was respect between them, but they never had the chemistry that Bolin did with Korra alone. Mako just seemed like he was too good for anything. Development is our middle name. It always is. 

A nice way of putting it!

Without a substitute fire bender on hand, Bolin and Korra couldn't play (and I say that because I believe Korra is only allowed to use one element, Water, otherwise it wouldn't be fair that she can switch elements and get a substitute that's available for water and all). Mako and Asami can use the next night for each other. They'll hear about the attack the next morning or in the middle/near the end of it. It's Mako's 'repair what I have fractured' night, so he's going to try not to get distracted.