On Valentine's Day, I sent her a short message and a multimedia message, but my girlfriend didn't reply.

It's okay. Maybe she is busy or she is testing you.

I often encounter this situation!

You must not mention this when you meet! Pretend nothing happened.

After she sends you a text message, you can put it off for a long time (but you must return it).

Let her know that you are not easy to bully.