All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Abu Hurayrah narrated that the Prophet said: “If a man whose religion and moral conduct are pleasing to you proposes to you, then let him marry; otherwise there will be great mischief and corruption on earth. They [companions] asked: “What if he has something to be criticized about.” He said: “If a man whose religion and moral conduct are pleasing to you proposes to you, then let him marry (and he repeated this thrice).” [At-Tirmithi]
Therefore, this Hadeeth indicates clear guidance towards responding to a betrothal from a person who fits the Islamic characteristics and that refusing him will contribute to trials and conflict, which are a direct result of a marriage to a person who is not religious. We, therefore, advise you to covet eagerly the person who is religious, as marriage to the latter [whom you referred to as M.M.] does not guarantee prosperous results which may be the cause of your upsets.
Furthermore, rather than guiding him, he can be a cause for leading you astray, since it is usually easier for a woman to follow a man rather than the reverse, and the callers to evil outweigh the callers to goodness in this day and time.
Allah knows best.