Is a married man sinful for loving a married woman whom he cannot marry, even if he does not commit any Sharia violation?

It is not permissible for a person to attach his heart to a foreign woman and indulge in thinking about her, because inner thoughts can lead to sin through the entry of Satan and the temptation of the self. The Prophet, peace be upon him, mentioned that the heart desires and wishes, and this is a means to adultery. However, if the love is merely a feeling in the heart and one does not act upon it, then there is no sin in it. What is obligatory is to fear Allah and divert oneself from thinking about this woman, for a Muslim's heart should not be preoccupied with other than his Lord.