Whether or not to self-forgive in the context you describe may depend on the answer to this question: Do you feel guilty in any way? If the answer is “yes,” then the next question is whether or not this is genuine guilt or a false form of it. Sometimes, we falsely accuse ourselves and upon further examination, we realize that we did nothing wrong. If there is a sense of genuine guilt, then there likely is a sense of wrong-doing. What is the wrong-doing? Try to be specific. You say that you should have seen the signs of a poor relationship coming. Yet, you did nothing intentionally wrong here. As you call it, stupidity is not a deliberate intention to do wrong. And sometimes we just do not see tragic flaws in others until we know them in the greater depth of a marriage, for example. So, are you experiencing genuine guilt? If so, forgive yourself. If you did nothing objectively wrong with a bad intention, I would recommend that you try to be gentle with yourself, to be merciful toward yourself, but not necessarily in a context of self-forgiveness in which you see, acknowledge, and correct a moral wrong within yourself.