In this clinical case we describe the sex therapy of a young man with situational erectile problems without concurrent comorbid problems. The intervention had a ‘blended’ design, with online contacts, face-toface sessions and between-session contact through email. The clinical assessment was set up as a collaborative project of therapist and client. The case description is illustrated with verbatim text fragments selected from an evaluation report that the client wrote after termination of the treatment and sent to the therapist. The use of the text fragments was explicitly approved by the client before manuscript was submitted. Special attention is given to the use of a simple online monitoring instrument. Next to a description of the instrument, the procedure to adapt the monitor for use in specific therapeutic settings is described, using an online questionnaire system. We also described the statistical tools that can be applied to visualize the monitor data and to statistically test treatment efficacy. The monitor is made available in open source R package ‘userfriendlyscience’, and a (Dutch) tutorial is available at https://osf.io/6afhs/.