In terms of Celebrations, in Islam we have two days which have replaced anything else. At those two days we celebrate is Eid Al Adha And Eid Al Fitr
Anas (RA) reported that the Prophet (SAW) came to Madeenah with two days they played in. The Prophet asked: 'What are these two days?' They said: 'These are two days we used to play in in our Jaahiliyyah'. The Prophet said: 'Allaah has replaced them with two better days: Eid Al-Adh-Haa and Eid Al-Fitr'"
Furthermore if you look at the origins of 'valentines' day - I mean really researching where it comes from its far away from our deen of Islam. It originates from disbelief, and yes Shirkh. Celebrating it this day means your just following just that, it would be foolish, for those who don't know and for those who do.
If you want to show your loved one that they are dear to you, pick another day. Be different to the disbelivers in your affairs, especially something like this.