Is my sister a ?

my sister has recently been thru a breakup (wit a guy) and now her and her "best friend" are acting strangly they are permanently holding hands and spending alot of time alone together. they hav forgotten about evryone except each other. they r planning their life together like holidays and uni but hav only known each other 4 a year....they cuddle on the couch and grab each other evrytime they laugh. they also dirty dance together and grope each other. evryone is worried about them.the best friend also worryingly gets bored of guys in a matter of days.