Gabriel has always loved God's creation more than anything... Except God of course,But there was something about You, that surpassed His love for His brothers and God...He found Himself feeling protective and afraid of You getting hurt. You two got along and realized You had a lot in common. After some time Gabriel got abducted and tortured by Asmodeus,Who used Gabriel's grace to get stronger and it went on for few years till Ketch brought Him to the Bunker.Cas and Sam tried to feed Him his grace but He refused to take it due to the trauma,He endured so they thought maybe You could get Him to take it