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.

Also recommended:

Kiss Me Like You Mean It   by Dave Clarke

Related Article:

Avoiding Emotional Adultery  by Judy Starr