I have been dating my boyfriend for 2 years, and something is wrong...?

We've just celebrated our anniversary on the 27th of this month, and the happiness of our relationship's accomplishment, lasted a few blissful moments..... because now, it seems like he is losing interest in me. It's not like he's used me, because the typical cliche of a guy dating a girl for has nothing to do with this case.... he just seems to not love me the way we used to. More and more he's talking to other girls..... and i'm as hopeless as to stand beside him and listen, and experience jealousy.... :( Does someone out there in this world understand what I'm saying.... I can't believe love can be so grueling.... :((