I did not read this thread from the top, nor did I read all posts. In scanning random posts there seems to be a focus on tsnius (or lack of it) and its impact on shalom bayis.
Someones elses spouse, or even single members of the opposite gender are likely not THE cause of issues, but may be the outlet used. Aino domeh mi shyesh lo pas bisalo, limi shain lo. Perhaps counseling in this area is something couples should look into, so that their spouse doesn’t look to fill his or her sal with forbidden fruit.