Does slip of tongue reveal emotion?

I have a feeling that my boyfriend fancies my younger sister (let’s call her S2). We were sitting in the car the other day talking about my eldest sister (s1) then he mentioned smth like “you shouldn’t tell S2 I mean S1”. This isn’t the first time happening. I have 2 other sisters and never heard of their names come out of his mouth except for S2
Does slip of tongue reveal emotion?
Post Opinion