Risking sounding inconsiderate here - I would say it is time to reframe the relationship in your mind. Sure - you coulda, shoulda, woulda had that great relationship with your best friend and lover if only....
We mourn the "if only's" and they aren't real.
It has been amazing to change my perspective to reality. And my reality...I don't even like this person. Ugh! And I force myself to keep that in the forefront on my mind, overruling my emotions of missing the "coulda, shoulda woulda beens"
And lastly - your BF is at least wise enough in his disease to recognize he can not give you what you want and deserve so take his advice! You loved him genuinely and authentically - he is not ready for that - you are in the prime of your family-building years...don't waste any more time on someone who is not where you are in life.