I decided to elaborate this simple map because I realized Europe is almost divided into two blocks: same-sex marriage is recognized in whole western and northern Europe (except Northern Ireland, Andorra, Monaco and Åland) but it does not exist in central and eastern Europe.
Years when it came or will come into force are shown respect each country. Different colors for each lustrum.
I'll update this map if other countries change their laws in future.
EDIT (30/06/2017): Same-sex marriage has been legalized in Germany.
EDIT (14/07/2017): Same-sex marriage has been legalized in Malta.
EDIT (23/06/2018): Same-sex marriage will become automatically legal in Austria in 2019 because of a decision of its Constitutional Court.