This article is from the BiSexuality FAQ, by Jon Harley email@example.com with numerous contributions by others.
No. People who call themselves bisexual are saying that they are attracted to
both men and women. They don't necessarily have to act on that attraction, any
more than straight or gay people have to act on their attraction to people of
the same sex as their partner.
There is a separate newsgroup, alt.polyamory, for discussion of the issues
relating to the dynamics of multi-way relationships (whether involving
bisexuals or not).