Does divorce befall the second wife if the husband utters it during intimacy with the first wife, while he does not intend divorce, but rather says to himself, "O Allah, no"?

If you utter a kinayah (allusion) of divorce without intending to effect a divorce, then it does not take place. However, if you utter an explicit statement (sareeh) of divorce, then it takes place even if you did not intend it, because an explicit statement of divorce does not require intention. If one divorce (out of three) has occurred, you can take your wife back during her 'iddah (waiting period). It must be emphasized that a woman is forbidden from seeking the divorce of her co-wife, and the husband should not comply with his wife in this regard, but rather act with wisdom.