Am I obligated to return the ring and the money to the suitor from whom I separated and who married another woman, and what is the ruling on donating them to the mosque to absolve myself?

If the ring and money were given as a gift, then there is no obligation to return them, and he is not allowed to demand their return, based on the Prophet, peace and blessings be upon him, who said: "The one who takes back his gift is like a dog that returns to its vomit." However, if it was part of the dowry, then it must be returned. As for the money, if it was a trust and you were permitted to use it on the condition of need, then you must return it to him upon his request.