it sounds to me like you can't simply be his freind right now...which is OK by the way
hoping to show him how great youa re or proving how much better he is with you or praying that he will be more than friends with you again
is NOT no expectations
no expectations means just that
if you can not be this then do not try right now
revisit the option later when you have let go more
it is not vital for you to be friends with him
sometimes they are people we would not ever want as friends
pray for him that he finds his way to happiness wherever that is true happiness
and be a friend to yourself
don't push yourself to be someone you are not you do not need to martyr yourself in order to be his friend
perhaps the most loving thing is to not be his friend, to not enable his choices, to prove to yourself that you are more important than how he is treating you, to impart this lesson on to your child
perhaps the most loving thing to do, since you can not be his friend with no expectations is to not be his friend...not that I am saying be cruel to him i am saying pray for him and keep your distance for you and for him and for your son
keep your emotional distance so he doesn't feel the pressure of always letting you down by not giving you want you want so that you don't always feel let down and hurt that he can't see how amazing you are so your son sees what an emotionally strong person looks like