This guy is a tease and I, too, would be upset for him to be making jest of what I see as a serious step in a relationship.
To tease you multiple times by getting down on one knee to pull your emotional chain is cruel and fits under the category of emotional abuse. Sorry to say. I am going to, just for a moment, play the devil's advocate and defend him...maybe he is pulling this crap on you so when he really does ask, you will then be surprised because right now he is numbing you with false hope, so when it is for real, you will be shocked. But, seriously, what he is doing is tainting any proposal you can have that is real.
I would sit him down and tell him that a proposal is no joke and if he does it one more time, you are going to leave him. MEAN IT. How dare he dangle that carrot in your face time and time and time and time again. Even lying about buying a ring? He is so immature...do you really want that for the rest of your life?
From today on, please pretend you are a stranger and looking objectively over how he acts and behaves on a daily basis. Without emotion, just take an objective look at how he conducts himself, how he treats you, how he is or is not a team player in your lives. Being the "fly on the wall" as you observe yourselves together may help you realize that this IS the guy of your dreams or he really is not the guy you want to believe he is.
Trust me, you need this exercise.