@lukasmandl from pragmatical viewpoint the reason for the continuation of ties with Putin's Russia is probably economical. If I am not mistaking Serbia enjoys open access to Russian market and since it is not an EU member Serbian companies would find it hard to compete on EU markets due to the trading barriers. Handling of Kosovo is a different topic. Serbia does not view Kosovo as it's neighbor but as an integral part of Serbia. But it is more complicated than that. Regardless of how we view the right of the Kosovo to the independence (NATO campaign in 1999 lacked UN mandate etc...), today Kosovo is de facto independent country and steering nationalistic sentiments on the both sides is the cheapest trick in the book for redirecting attention from the real issues, one of the being mass emigration of youth from both Kosovo and Serbia to EU countries.