Notes from my Legal Ethics text...
The Model Rules of Professional Conduct have loosened a bit on allowing spouses to represent opposing clients (a prohibition now allows clients to give informed consent). One reason given is that approximately half of new entrants to the bar are women, and half of female practitioners are married to attorneys!
In 1992, California became the first state to establish a rule against attorney-client sexual relationships. The ABA has since adopted a similar rule, and the comments argue that the client's emotional involvement prevents them from giving informed consent to this combination of sex with a professional relationship. The text editors ask, "Does it follow that only emotionless sex is truly consensual?"
Deborah L. Rhode and & David Luban, Legal Ethics, 4th ed. (2004).