Putin is basically in a situation where he made a move that worked well for him (seizing Crimea), but unintended consequences are backing him into a corner. Specifically, he really didn't plan on the Donbass rebels rising up, since unlike the Crimean seizure he really can't win. Up to now he's basically been trying to keep both anti and pro war Russians happy, and it's worked; anti war Russians see that Russian troops aren't pouring into the Donbass and fighting Ukrainians, and they're happy, while pro war Russians hear of covert operations supporting the rebels and they're happy too. However, since the rebellion has gotten so bloody and it's unlikely things will ever return to normal, Putin is looking at a bunch of negative scenarios for Russia, regardless of how things go and ignoring what the US/EU do.
Previously, taking Crimea didn't necessarily destroy Russo-Ukrainian relations for all time, nor did they destroy the foundation of the Ukrainian state. Putin would have probably preferred a peaceful annexation of Crimea followed by the Donbass using their electoral influence to prevent EU supporting westerners from completely cutting ties to Russia. Instead, in his best case scenario, he gets a very unstable, overstretched pseudo-country on his borders that desires to join Russia but has little to offer economically, especially after a devastating war, as well as the enmity of what remains of Ukraine. Worst case scenario, he ends up with a hostile failed state on his border in a constant state of chaos, possibly spilling into Russia on occasion.
I think a lot of you guys are giving Putin too much credit as an evil mastermind plotting the wholesale annexation of Ukraine via Russian agents in the East. Probably at first he had nothing at all to do with the rebels and simply wished they would go away (though he couldn't say such a thing with many Russians sympathetic to the rebels). However, the strong fight put up by the DNR/LPR, aided in part by many adventurers crossing the border to assist, made it really hard for Putin to throw his hands in the air and do nothing. So he's basically operating according to Russian public opinion at this point, as opposed to any sinister plan.