If you have a "hateful feeling" when you see the person, then you have not truly forgiven them. (no judgment--just stating the facts)
I think that just because you forgive a person doesn't mean that you forget what they did, or try to forget. That would be impossible and/or foolish in some cases.
I do believe, however, that forgiving them helps YOU, though they may not need or care about the forgiveness.
Particularly if these were bad/traumatic experiences, you may need therapy to help you work through it. Therapy is not a bad thing or a dirty word! Its just a tool, though a psychological one, to help you on your road to good health.
This is pretty mild, at least compared to what you hinted you went through, but I had a friend, who I thought was a very close friend, betray me. It took me a long time to forgive.... and part of that was forgiving myself for trusting someone who was so self-centered. I never trusted her again, but I was able to at least treat her with basic decency and courtesy. And I felt better having forgiven her for her failings and for forgiving me for mine.