Why is my friend like this ?

She's clearly ually immature - but the truth is she could also be unsure of her own uality also. Making fun of or making "eww" comments about same relationships may be a way of avoiding what she truly feels. This, of course, may not be the case - but I know I always acted creeped out by same relationships b/c I was afraid people would notice how fascinated I was with them instead.