On the one hand, it may show his persistence and firmness in love. This song may have touched his heart and made him feel the strength and firmness of love. He may use this song to express his views on love, or he may use this song to express his commitment and firmness to marriage or family.
On the other hand, it may mean that he has not completely let go of his past feelings. A married man may miss his old feelings, and this song may remind him of the past. In this case, he likes listening to this song because he hopes to release his feelings through this song, or he hopes to miss the good old days through this song.
In short, everyone's understanding and feelings are different, so to understand the meaning that married men like to listen to "endless love" needs to be analyzed in combination with specific situations.