Why do people think this kind of situation can end well?
You aren't the exception to the rule.
It will never end with a HEA.
And if, by some miracle it does, you best believe there's a hell of a lot of pain and suffering that will come before the allusive HEA.
Even if Prescott doesn't know it, from the moment the proposition tumbles from his lips there's no way in hell he's going to give Annaleigh up. From the leasing a house, the dinner party, even the photographs on the mantle... Prescott is in this for the long haul.
All he needs to do is convince Annaleigh that it's no longer just a deal between friends.