I am looking into the crusades, and was thinking as to whether this might have been possible. I'm sure the men didn't go away from their wives for that long without having some form of interaction with women, but would there have been love involved? If so, what would happen when they left, would it have been possible for a Muslim woman to come back to England with the knight, and if so what kind of reception would she have received? Equally, would it have been possible for the knight to have stayed? And more importantly, is there any evidence to show that this did happen? Any further reading, primary or secondary sources, would be greatly appreciated, either on this exact topic or on the crusades more generally. (Sorry for the multitude of questions within one!) Thanks in advance.
Love and marriage were different things back in the age of Crusading. I bring up marriage, because that is what I imagine you mean by "staying" with his new love. Until the mid 1700's marriage was generally used as a way to further your personal and family power. Love would either come later or outside the marriage.
Both Catholicism and Islamic law would not allow a Christian man to marry a Muslim woman. However, a Muslim man may marry a Christian woman as long as she was never a Muslim before.
The Quran in Sura 5:5: ...And chaste women from among the believers (Muslim) and chaste women from among those who were given the Scripture before you (Christians & Jews)...
This is likely because a Muslim husband may convince or force his wife to convert, but it would be bad business for a Christian man to force his Muslim wife to convert to Christianity. Muslim men married Christian women not infrequently in many places over many time periods, and still do today. There are many instances of it happening throughout Spain before the Reconquista.
Christianity is even more restrictive than Islam, generally forbidding any inter-faith marriage. Among a few other verses...
2 Corinthians 6:14: Do not be yoked together with unbelievers. For what do righteousness and wickedness have in common? Or what fellowship can light have with darkness?
That isn't to say special dispensations cannot be made by the Pope in exceptional circumstances.
During the 3rd Crusade, Richard I of England proposed that his sister, Joan of England, be married to Saladin's brother Al-Adil. Neither party seemed terribly keen on the idea of marrying a heretic, but it would not have been floated were it not possible.