All the planning in the world doesn't factor in that life throws some curveballs. I have a friend who dropped out of her PhD program when she got married (even though she stayed in town after she got married), and I know two non-academics who got married and lived in different states for almost a year 'cause she didn't want to make her kid switch schools for 8th grade. She moved to his state in the summer, but she'd never planned on moving out of town. Another friend (undergrad) has a girlfriend in a different country 'cause he met her while visiting family, and neither them can put their education on hold. I guess my point is that stuff happens, regardless of what you plan for 'cause life is unpredictable that way.
You're also implying that you can't be a phD student and have a relationship, which is just weird. A friends sister is getting a PhD, is married to a post-doc, and has 5 kids. Far as I know, they'd never really planned anything 'cause he was a grad-student and she was an undergrad when they got married.
As much as I do hear where your coming from, it's ridiculous to put your life on hold 'til you get a phD, post-doc, whatever. Nobody recommends that college students shouldn't date just 'cause they may end up wanting jobs in different states, but that also happens (as different fields are strong in different regions.)