do i have to get married to have rights even we have been together for 3 years? which state accept this legal law

If you're talking about common law marriage, there is more to it than simply living together.  You have to tell people you are married, introduce yourselves as married and file a joint tax return, and be together considering yourselves married for a "significant" period of time.  There are very few states that still recognize this, and Nevada isn't one of them.

The fact that you aren't married doesn't mean you have no rights, but they are far fewer, and for the most part are based on ordinary contract law:  if promises were made to you, and you can prove them, it's possible, sometimes, to have those promises enforced.

If someone is telling you that it doesn't matter, as an excuse not to get married, he's wrong.  You should talk to a lawyer, if you need a detailed review of your rights, based on the unique facts of your own case.  One place to find a qualified attorney is our website, http://attorneypages.com