Prompto saving Ignis from an arranged marriage by being like "Well, she can't marry you if you're already married, right?" He was half joking at first, they're friends! But seeing the startled look on the other's face just makes him commit to it because come on listen it's a good idea! #promnis

Ignis musing it over because it's tempting, it's intriguing, making the point that obviously Noctis is out of the question and Gladio- Only for Prompto to cut in, "Why not me then?" THERE'S SO MANY REASONS, the top of the list being that Ignis is already emotionally compromised over him.