Can you sue someone for the money you spent if they weren't present at your date?

I really hope this is not a serious question. The answer is no.

That's an interesting question. People have sometimes sued when an engagement has been broken. I have even heard of lawsuits based on prom dates being broken. Those lawsuits usually seek to recoup nondiscretionary expenses, such as the costs of the wedding hall or the prom tickets. I think it would be hard to sue for flowers and "new stuff," which I assume is clothing for yourself and other things to spiff up yourself and your car. Although our court system allows anyone to file a lawsuit about anything, I think this one would be considered frivolous and that you also may not be able to prove the date amounted to a contract. Also, by engaging in a lawsuit, you are seeking to prolong the relationship with her through contact in a court. That is not a good idea. It is time to move on to better things. The important thing is to never, ever pursue or accept a date with this same person again, because the same or worse will happen. She has not treated you right and it is time to move on to someone who will appreciate you.