Should I explain to my nephew the reason his mother isn't around is because of infidelity?

He is likely confused as to why his mom randomly just left his life, not that I have any problem with his estranged mother. I do worry about the effects of it like he might become a drug addict someday or something. His mom had an affair with her boss, got into a relationship from the affair, and the guy does not want her kids around or to be a stepfather.

Should I explain to my nephew the reason his mother isn't around is because of infidelity?
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