Once you have told your boss you’re leaving they‘ll lavish praise on you and tell you how you are meant for better things. Even if it had been true, it’s not now. You have promised your heart to another and that’s more than they can take. If they really loved you they wouldn’t be putting you through this and you would have had that promotion and pay rise you wanted a long time ago.
1) They don’t really love you! 2) They only want you because they’ll be lonely!! 3) They’ll get rid of you as soon as the next big thing comes along!!!