If you get an opportunity to mentor someone who is struggling with an emotional entanglement, the following resources could be very helpful for your use or for recommendations.
Hedges: Loving Your Marriage Enough to Protect it by Jerry B. Jenkins
Plant preventative hedges around your marriage … Practical ways to avoid compromising situations and giving temptation a foothold in your life. Jenkins’s real-life stories of how temptation can slip in undetected.
Kiss Me Like You Mean It by Dave Clarke
Avoiding Emotional Adultery by Judy Starr