I have 2 dates on valentines day and they have no idea how I can attend them both.
What are you planning on doing with those dates you have?
I'm going to say that I can't go on either of them as I'm busy.
You shouldn't string people along. That is very wrong to date two people at once and lie to them. You are being selfish if you do so and you are going to hurt their feelings.
I don't owe them anything so I can do what I want.
If you promised them that you will attend the dates, then it is absolutely something that you owe to them. If you do not really want to go to the date, being honest and cancelling on them is the more mature way of dealing with it, so that they can find other dates on that very romantic occation.