Any "The reason for problem X is just one thing" explanation is usually BS - or at least severely limited.

Reality is complex. Human beings are even more complex. Thus the majority of problems might have - and do have - LOTS of possible reasons.

Cheating is no exception: it might be due to lack of love, yes, but also to many many other issues (e.g. lack of connection, lousy sex or lack of it, bad communication, incompatible personalities, conflicts, hidden anger, emotional void - just to name a few).

Not to mention humans are not wired for monogamy - and this is true for women as well (they usually become "sexually bored" within a few years).

Simple explanations ("the ONE thing...") feel good to naive or small minds, because they're are reassuring; but more often than not they are wrong or misleading.

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> "If someone loves you, they will willingly marry you."

Also, the equation "Love = marriage" is extremely simplistic and naive as well. One might love several persons in her/his life (as many do); does it mean s/he has to marry ALL of them?!?

This kind of ideas pertain to fairy-tales much more than to actual relationships; it's kind of Disneyland. Again, it’s naive, simple-minded and childlike: it’s something a little girl would dream about, while an adult would realize it’s much more complicated than that.