My response to you includes a spoiler from this past series of Mad Men, so anyone who hasn’t seen the last episodes, turn away!
Don Draper starts a relationship with a woman named Faye during this series, but the more she got to know him and learned his secret, saw him throwing up and and not as the cool, collected persona he’s developed, started really caring for the man without the mask. But this was freaking him out and he started arguing with her, cheating on her and avoiding her. By the end of this season, he threw her over and immediately got engaged to his secretary Megan in a matter of days on a business trip, who is a woman he really doesn’t know very well. He breaks up with Faye over the phone and she says to him, “I hope she knows you only like the beginnings of things.”
What Faye meant was that Don likes the giddy, fantasy-strewn parts in the beginning of a relationship, when lovers don’t know each other all that well and they can project a fantastic image of perfection on the other person. That’s what “being in love with love” means, getting that oxytocin high. The more you get to know someone with their faults and foibles, that’s when some people come off the high and bail. I had a bf like that, and I didn’t realize it until I saw him go through the cycle with 3 other women. Then I felt less bad.