If I ask a girl to be my valentine does it mean I am asking her to be my girlfriend
If you keep in contact with her and go on a date, yes
not nessicarliy. going on a date and becoming a pair are two different things.
It does not mean you're asking her to be your girlfriend unless you ask her to be your girlfriend. Just the same way as when you ask her out, you're just asking her out to dinner or movies or to hang out...NOT TO BE YOUR GIRLFRIEND...