My husband is having an affair. Can you please suggest any Dua' (transliteration) which will get my husband back to me and be loyal thereafter. And all any Dua' so that he can be away from these attractions.

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

There is no particular Du'a in the Sunnah for this matter, i.e. to bring your husband back to you and to remain loyal. But the Shari'a emphasizes making Du'a in general, i.e. supplicating Allah for well-being in this Life and in the Hereafter as long as one does not ask Allah to help one commit sin or sever kinship. Allah Says (interpretation of meaning): {And your Lord said: "Invoke Me, [i.e. believe in My Oneness (Islâmic Monotheism)] (and ask Me for anything) I will respond to your (invocation). …} [40: 60].
So, Pray to Allah from the depth of your heart to make your husband love you and protect him from dissolute women and all evil and sins.
Moreover, you should exhort him, enjoin good and draw his attention to the bad consequences that occur through these illegitimate relations in this world and Hereafter as well. Remind him of the punishment of Allah for such bad practice. If he benefits from your efforts that is what you want; otherwise, you may request help from someone who has influence upon him to exhort him.
Likewise, you should spare no effort to be a good supporter to him to adhere to the right path and to come back to you. You may attain that by endearing yourself to him, beautifying yourself for him, serving him, and showing him your deep affection and doing other permissible acts.
Allah knows best.