Yes, but ... it is worth remembering that there is much more to a person, and to a relationship involving two persons, than his or her stance on monogamy. Our beliefs evolve and change over time, a polyamorous person might still casually date a “questioning” or “mostly monogamish” person, or a friend might be fully committed to polyamory but still have certain things that he or she would prefer not to share with a close pal. In other words, your friend might have boundaries that are unknown to you.

If I valued the friendship, I may have spoken first with my friend and alerted him to my plans. This isnʻt the same as asking permission, but it shows that you respect the relationship and his feelings. Just a thought.