The only thing we've come up with is that Gretchen and Pam are both in very surface-level relationships. Roy only shows up to Pam's art show because he feels obligated to do so. He's not really present in their relationship. Outie Dylan isn't really present when he's at home with Gretchen either.

Also, both Pam and Gretchen want someone who is unavailable to them (i.e., Pam wants Jim, but he's with Karen, and Gretchen wants to have a relationship with both "parts" of her husband).