What if I used to be a nice guy?
I don't understand. Why do you feel you used to be a nice guy? What did you get out of it?
I used to be a nice guy when I saw that people appreciated my help
When doing favors for people you should not expect anything in return. It is sad you would stop helping because people do not appreciate your helpfulness.
But I only wanted recognition from help. I was so powerful then.
It doesn't sound like you had good motives for being a nice guy, so you were never a nice guy. You should treat people well because people deserve to be treated well not to get things out of it.