Firstly, I don't think you are manipulative or a sadist, if only judging by the few postings of yours that I've had the privilege of witnessing.

Secondly, even if you were, your remorse for such actions is evidence that you're not a bad person. Everyone manipulates and has angry thoughts to some extent. That doesn't make them bad people. Intentionally hurting others and not feeling bad for it or changing that behaviour, on the other hand, does indicate a rather unsavoury individual.

Thirdly, being manipulative, cold, and sadistic does not make you bad person. If one can use those skills in a morally acceptable manner, there's nothing wrong with having those skills at the ready for the opportune moment. Sadism doesn't even indicate a morally corrupt person as long as said sadist has a consensual partner.

Lastly... If anything should happen where you have hurt someone and feel badly about it (again, this guilt indicates that you have conscience), don't hold onto that guilt and punish yourself. In the end, that won't help anyone; it will only harm you. Instead, learn from it.