Thanks for your interest in this story! I'm not sure how many people will actually read this but this is for all the readers who actually are interested in what I have to write!
The shift from Generation X and Generation Y is very interesting. With respect to the way romantic relationships are handled, at any age is very different.
A huge contributor to this issue is Hollywood and the media. In the past, movies had this notion of a "Prince Charming," who displayed chivalrous acts, and gestures.
The gradual shift, or rather, a quick shift (depending on what you define as quick) to a different model of how Generation Y handles relationships is reflected in Hollywood and the media.
Due to these notions in movies, the ideas become entrenched within society, especially for the younger generation. The shift from movies like, "A Cinderella Story," starring Hilary Duff and Chad Michael Murray, versus modern-day contemporary movies such as, "Friends with Benefits," starring Justin Timberlake and Mila Kunis or "No Strings Attached," with Ashton Kutcher and Natalie Portman is a significant contributor to the reason why relationships have changed.
This former model is presented to millennials as a very closed minded and more conservative way to date. Millennials are also currently watching the divorce rate climb rapidly. The divorce rate is sadly more than 1:1 marriages.
Something important to mention here is consumers. You're probably thinking, "consumers, am I reading the right story?" I promise you, there's a connection. Historically, especially in previous generations, there was a notion of not discarding of anything until you really needed to. Remember your grandfather saying that fridge still worked? Even though you would've gotten a new one? The new generation finds that manufacturers already estimate when the product will break and banks on the fact it'll break so the consumer will need a new one.
Much like technology, there's an idea of something "always better coming". Which can be compared to relationships and the reason why people skip from relationship to relationship.
Interested? More to come :)