Does he like my sis?

My boyfriend acts like he likes my sister more than me. My sister thinks he's just being nice but I think he likes her. When she comes in my room with him here we stops cuddling till she leaves and talks to her a lot while she's in there or if I go to the bathroom he goes and talks to her if her door is open or if she's in the living room. Iv said something to him about it before and he just got mad and said "what am I just not supposed to talk to her? Your just jealous babe. " what do y'all think? :/