The Sims 3 : Can't do the romantic action

I try to make my sim have a relationship with another but on the Romantic option I can do just 'Flirt' 'Hold Hands' 'Amorous Hug' and some more. Even I repeat all of that and the tab is full, both sims are just being 'best friend'. They can't even ask each other on a date !!!

but if I get them on a couch they still can kiss and make out (also in bed) but there's still no heart sign occur on a relationship status

is it a bug ? or what have I done wrong ?