Does a letter forgiving an affair matter for AA/CC?

My stbx wrote me a long letter forgiving me for an affair. It states very clearly that he forgave me, wanted to work it out, believes the affair is a result of how he was abusive to me. I believe this could be used as condonement of the affair even though we separated a month later, which would impact a claim for alimony as the dependent spouse.

Could condonement of an affair also be used as a defense to a civil AA/CC claim on the 3rd party?

The condonation can be used as a defense for by the third party for an alienation claim.
(ie, the actions of that third party did not destroy the affection in the marriage) however criminal conversation is a strict liability tort, meaning forgiveness within the marriage, fault, or even no knowledge of the existence of the marriage are not defenses.