Ok, now about inlaws, when should you start caring? There are two different schools of thought on this.
Love first, family second or never
Worst Case: Romeo and Juliet, (unless you think everyone in the entire world knowing your business long after you're ded is a good thing)
Best Case:Mr. and Mrs. LaVerio down the block. Their families HATE each other, always have, but they didn't care. Everyone else is dealing with it, they're going on 60 years married, still laughing their a**es off at everyone.
Family first, love no biggie
Worst Case: My sister in law's little sister married the guy down the street because the families thought that they were perfect, and she ended up in court after trying to stab his eyes out with a salad fork from the silver set she got from his granny. Mess.
Best Case: Beauty and the Beast. She did her thing with the monster to save her dad's hash, and ends up with a rich, good looking guy. (warning, this is the best case,most time what eventually gets revealed is less pretty, with worse manners)
Nine times out of ten, it doesn't predict actual happiness. So suit yourself on this one.