The Golden Couple by Greer Hendriks and Sarah Pekkanen

A married couple comes to Avery, an unconventional therapist, to save their marriage. Marissa has had a one night affair and will do anything to redeem herself in Matthew's eyes. Avery takes them on as clients and schedules eight sessions all the while digging deep in their personal lives. The biggest secret that Marissa hasn't shared is that her one night stand won't let her go and is constantly texting, leaving gifts etc. Each of the three have secrets. Each of the three knows the cost of keeping them and each of the three wants them to go away. You want to feel sorry for one of them but as you learn more you are thrown off balance. We all want a happy ending and these seasoned authors are very good at misdirection and giving you that happy ending but it might not be the one you expected.
Well paced and expertly delivered this writing team knows that first impressions can be deceiving.  4 stars