The fact he was unaffected by the curse I think helps in the compatibility department. How else are they compatible let me count the ways: 1) They both lost loves in the past 2) They love the children in their lives 3) Robin was clearly brought up as a gentleman “chivalry and all that” and Regina a lady “never misses her teatime” 4) Both have a dry sense of humor 5) Both have reasons not to include Rumple on their X-mas card list 6) Both know how it feels to be persecuted by others 7) Rob has a calming presence that could bring down Regina’s fiery temper 8) Rob knows the value of family 9) Rob is not unfamiliar with magic and its limits 10) Rob fights to save the lives of those he loves
St…you’re the best!
"If you go as far as you can see...you will then see enough to go even further." - Finn Balor