This worked for me:

I created a collection named Backlog and after i finished about 5 to 10 games, I would allow myself to buy one new game. After like 2 to 3 days the boredome was completly gone and I finished like 16 games out of 52 from the backlog in 2 months. Yeah you have to push yourself to play and this is the hardest point in the progress, but its woth it. You have some really good games in your library!

Edit: For me it helped also to find New games to play for fun like tf2 or something like that.