Letting Go of Toxicity

I have let go from three formerly good friends in the last year, and frankly sometimes I feel a bit cold for doing it, but they were toxic for me, it was for the best as sad as it seemed at first. Do you hold onto friends just because they've been a part of your life for what seems like forever because they've been through some hardships with you because they were seemingly there when you needed them? Or one day, do you decide to let them go because of their self-centeredness because of their jealousy because of their innate anger and fear of the world because of their ability to suck all of the positivity and energy out of your soul. All in all, I would rather concentrate my energy on friends with whom there is a natural, unexplained symbiosis ~ simple as that.