He wants to have a sex with me, but my mom will know sooner or later

DON'T!!! He just want's to get into you for his score card, don't let him.

Honestly, wait till marriage. Right now, at 16, you're not quite mature enough for the big one and rushing into it isn't a good idea. So don't have sex right now and tell this boy that you would rather wait (and if he doesn't respect you, dump him.)