Hi, I'm almost 25 years old, I had my first two gardasil HPV shots in 2008. Do I have to get the last one? Is it a must? I'm married and I only had 1 sex partner in my life and I'm not going to have more, he is healthy and me too.

Yes. The recommendation is to get all three hpv vaccinations so you are protected from the most harmful hpv viruses. Please get the third dose so you will be protected. You don't know what the future will bring and it is best to be all the way protected!
You . You have some protection from the first two shots and the third would boost that protection. If you are married and have only one sex partner, you will only be exposed to what (if anything) he carries. If he has latent infection with herpes or human pappiloma virus, you probably would have it by now anyway.