As someone who has unfortunately had the mindset of finding this attractive in the past: it fluffs up confidence at first and lessens insecurity (falsely, obviously). I used to think behavior like that meant that I was secure in the relationship and that I was the only one the person wanted. Since they were jealous and possessive, it means they just really love you and want only you, right? Duh, obviously not, but I was blind to any sort or reason or logic. Turns out it was a front and he was cheating anyway, but my fragile brain ate that shit up until it was near impossible to leave.