Curiousity

I am curious about something. How long does it take to get over the anger and bitterness in regards to someone you trusted who betrayed you?

I have tried really hard to understand and forgive things, but when it comes to anger and bitterness it is really hard to let it go so easily. When a cut is deep it takes longer to heal, which is common knowledge, but when it is a deep cut to emotions. How long does it take to heal?

I mean it has been years, heck decades, but yet the anger and bitterness still leave a bad taste in my mouth and thoughts. I was recently told I could hold a grudge like no other. However, I am unsure if this would be considered a grudge or just the type of betrayal creates the kind of anger and bitterness which is beyond grudge status.

So, the question is: Is prolonged anger and bitterness always a grudge or does it depend on what causes the anger or bitterness which determines if it is a grudge?