fkin feelings

I just left a 3 year relationship because it was unhealthy and I've been moving on for months. I stayed because I thought we could make things work, but I'm just unhappy. For the last couple months I've been really into my now ex's friend. He's nicer, more mature, and we get along so well. He's been making me so happy, but I feel bad for liking him. Does it make me a bad person to be falling for my ex's friend?