Is it better to fast one day and break the fast one day, then stop upon marriage and make up the missed fasts later, or to suffice with fasting Mondays and Thursdays, then advance to fasting one day and breaking the fast one day after marriage?

Fasting on alternate days (the fast of David) is the most beloved fast to Allah, and one should hasten to observe it whenever possible. If a Muslim stops this fast or limits himself to fasting on specific days (such as Mondays and Thursdays), this does not diminish the reward for what he has already fasted, as its continuation throughout life is not a condition for receiving the reward. One can return to the fast of David later without making up for what was missed. A condition for the virtue of this fast is that it should not weaken the body from fulfilling the obligatory rights owed to Allah and to people; otherwise, abandoning it would be better.