Is it permissible to divide the making up of approximately one hundred days of fasting over two or three years, or must they be made up before the coming Ramadan, especially since the questioner is about to get married?

You have erred by delaying the making up of Ramadan (definition) fasts for years. You must determine the exact number of days you owe and make them up before the next Ramadan. It is not permissible to make up the fasts in installments or to delay them when one is capable. Whoever intentionally delays making them up without a valid excuse until the next Ramadan begins, must make up the fasts and feed a poor person for each day. If the delay was due to forgetfulness or ignorance, then you only need to make up the fasts. The expiation (feeding a poor person) does not multiply with the repetition of years. If you find extreme difficulty in making up the fasts before Ramadan, it is permissible to adopt the view of the Hanafis, which allows for delay.