Oh, that sounds so hard for you, raised that differently and with them so unusually close. I would try to remember that he is as loving and as good a hugger/cuddler because of his early experiences? You don't have to be jealous of his sisters because he's "yours" at the moment and his love is not limited. I'd maybe go see a counselor on your own about your childhood experience and maybe see if you can get to know his sisters better, on your own and chat with them?

I remember when one of my brothers brought home his new girlfriend who became his second wife and I was always comparing her to his first wife (didn't like this second one, she was very shy/not "friendly" or "fun" in the same way the first one had been). I wish I had not been as young and could have gotten to know her better for herself and learned better to respond to what was there instead of what I wished was there?

It sounds like your boyfriend's upbringing was good for him, something he enjoys and I would not try to change it; like my therapist once said to me when I complained about my boyfriend's (now husband) behavior -- "How long have you known him? And how long has his mother known him?" :-) If you were to marry and start a family of your own, he would have to become more involved with you than his sisters but right now, he can still have the warmth of both?