I think I like winning too much. I keep calling and investing money in obviously losing hands in a desperate hope that "maybe he doesnt have it".
...and after I have lost yet another stack, I keep thinking "I knew that he had it, why the hell did I call?"
Is there any way, some mental excercise or something how to treat this problem? Please help!
Try to learn the art of folding. I think its what most successful players are known for.
I was in the same situation as you some months before. Try to read some more articles on post-flop play, as it seems like your weakness lies in post-flop play. 1 tip can be to be aggressive pre-flop which will give you some additional strength when you see the flop.
The only thing you need to do as a poker players is make good decisions in the long run...
If you know it's a -$EV call, just fold.
one hand on a flop such as 2 5 8 off and I had JJ on a preflop raised pot I also new probably I am behind as he reraised... he showed QQ... as I knew better than me ♦ good players mostly have the hands you think of cause they are good players and would not push all in with a8 especially they would not raise it preflop... 
other hand i had AQ and he showed AK... it was with higher blinds (in DON) and I knew he could not hit... but why should he raise all in on flop except with AK???
yeah... easy fold!
another thing to remember too is poker players hardly bluff. i find bluffs normally are played when no one shows strength on board. now if you get checked raised or action and they fire back, think too yourself they have something or better.
Just fold
