You need to want only them.
It's probably not a surprise to hear that Scorpio's tend to be a little rough and a little jealous... and beneath all that aggression lies someone who is secretly a little insecure. To quell that worry that they aren't good enough (and ultimately win them over for good) you need to convince them that you only want them, and you are not going to ever want anybody else as much as you want them. The more secure they feel with you, the more they will open up.