Your idea of getting ready for a date is throwing on some clean sweats and slapping on a little lip-gloss.

You've stopped blow-drying your hair straight -- instead you just twist it up in a makeshift bun with your scrunchy.

You can't remember the last time you worked out -- all you know is your skinny jeans must have "shrunk" in the dryer.

Those pretty lace thongs you used to wear? They've been replaced with pilled and faded briefs.

Yes, there are many signs that you've crossed the line between being comfortable with your partner and totally letting yourself go. But before you head down this slippery slope in your next long-term relationship, you should know that rocking the slob look is a form of relationship suicide for many couples. It invariably leads to straying, deeply rooted resentments or worse: bad sex.

"The most fatal thing you can do to a relationship is take it for granted," says Dr. Carol Cassell, a health scientist who specializes in the field of sexuality and relationships. She recently wrote a book that addresses the dangers of getting too comfortable called Put Passion First: Why Sexual Chemistry is the Key to Finding and Keeping Lasting Love.

"I don't mean you have to be on your best, goody-goody behavior all the time and get the full makeup going on every single day. But you do have to not take for granted that your partner will always be attracted to you, and that that it will always be a great relationship. You have to work at it.

"I think a lot of women sort of think, 'Well it's done; it's a done-deal,'" she adds. "But really, it's never a done-deal, and you really have to take a look at what you're looking like. In my book I talk about putting a 'bow on your package.'"

And she's not just talking about women. Many couples let their looks slide together. That's something Stan knows all about. He and his girlfriend of seven years grew fat together. It didn't happen over night, mind you.

It took many nights of ordering in and many days of not working out for them to morph into an unhappy, super-sized couple. And as in most cases, there were underlying issues in the relationship that led to their slovenly rut. But packing on the poundage only exacerbated these problems -- which eventually led the two Vancouver scholars towards calling it quits last year.

"Sometimes when you're in a relationship," says Stan "it has a center of gravity to it -- a friend of mine described it as 'the black hole' and it sucks in all energy and all light and nothing can escape it. I think that was part of what was going on with us.