When Does Grieving a Past Offense Become Bitterness

Question: My spouse hurt me very badly by having an affair. As a result of that we lost many things -- a large amount of money, trust, and peace of mind to name a few. Admittedly, I am really struggling. Several friends tell me I'm bitter, but I think I'm in the midst of grieving these losses. I don't deny I'm angry, but isn't anger part of the grieving process? How would I know if my grief was degenerating into bitterness? Is there a time limit (expiration date, statute of limitations) or some kind of emotional temperature gauge?
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