I have known people who have been threw this. The man who had two women, and a woman who had two men. Each partner hated the other partner. Nothing surprising.I asked them if they loved both partners, and they told me that they did. So, I guess that you can do it, but if you do do this be prepared for tons of drama. What was interesting about both these two different situations is the fact that I asked them both, "If one of your partners wanted to be in a relationship with another partner, how would you feel about this", they both told me they will not share.