Thank you for the responses.
I realize he probably doesn't want to make her feel like he's not there for her 100% when he is away on a weekend with her. But then doesn't this mean that being in a polyamorous relationship involve feelings of loneliness when the other person decides to go 'ghost' on you? Does this mean his encouragement to date other guys is what my solution could be for when he is away?
I'm still learning.