Honestly.., he just lacks experience..
This is a guy who lacked the confidence and self esteem to get into relationships with women he really liked.. He always felt like nobody liked him.., rejected.., unwanted.., and this lead him to eventually question his own value to others and his own self-worth..
You might actually be either the only.., or one of the few.., women who has given him the chance at a relationship.. Since he believes that he may never find what he has now again.., he's feeling insecure.., he wants to feel secure in knowing that he is great.., that he has some value.., that you like him for XYZ reasons and that he monopolizes those qualities in the dating market.., he is the best..
Yes.., this kind of insecurity almost reminds you of a little girl.., but he's you're bf now.., so I won't go any further to say something bad or negative..
Possessive? No..
Envious of you.., jealous of you and others.., constantly wanting attention and praise.., needing validation.., afraid of losing you.., Yes..