Someone who only wants to stay in or be part of a relationship, whether official or unofficial, for the duration of the honeymoon stage. Once issues come up, they could care less if the relationship ends and they get left.
Mutual Friend 1: "So, whatever happened to Jack and Jill? Are they still talking or are they finally going out? I noticed Jill was ranting on FB and Twitter the other night."
Mutual Friend 2: "Oh, they don't even talk anymore. Guess Jack is a honeymooner. Doesn't know how to deal with problems, big or small, when they arise."
1. Sex between a male and female where the male has sex with and ejaculates in the females belly button
2. Often performed when partners run out of other sexual acts to practice. Hence, the name "honeymooner" because by the time you reach your honeymoon, you'll have to break out the honeymooner.
Things were getting a little stale after 5 days of sex on our vacation, so I broke out the honeymooner.