Four years back I had sex with my boy friend once in a month or in two months now he got married with other girl my question is if I do marriage with some body else than that person came to know that I am not virgin or what should I do

So in the US, Canada and most of Europe, you do nothing, since it would be rare that you would be a virgin at marriage, in fact if you had not had several partners it may be less of a norm.

So I will have to assume you live in a country that has rules about being a virgin at marriage.

So while I don't ever say lie, you don't mention it. Many girls don't bleed when they have sex the first time, so he will really just not know.

But being truthful and finding someone that cares for you, and will marry you anyway, would be best bet.