Assalamu allaicum wa raahmatullah wa barkatuhu
We iyaki dear brother. Alhamdulillah, I agree with you. And especialy it is very importante to warn other Muslims about non Muslims celebrations and imitating thier costums, as they are not part of our religion Islaam,and it is forbidden for us to imitate unbelivers celebrations or costums. And Allah knows the best.
Dear brother " Sanan Khan", I do not know exactly which story is related for the " Valentines day", but from how I know, there are some romantic stories related for " Valentines day", and that this celebration is of Christian orgin and the day is named after one or more early Christian martyrs
Saint Valentine and was established by Pope Gelasius I in 500 AD. That is why this is a Christain celebration,and Muslims should not imitate kaffirs.
And Allah and His Messanger sallahu alayha wa salam knows the best.