Who loose money when we win or make profit form forex trading?

When we make profit from the forex trading, who loose? Or from where the money come from? Forex trading is not like share trading. In share trading there are buyer and seller with the exact quantity and specific contract for trade. When you buy share you are paying money to the seller indirectly, which meant if he make profit, the money come from you as a buyer. Whereby in forex trading there is no specific contract or quantity to trade. So my question is if you make profit in forex trading where is the money come from? Let say i buy 1 lot EURUSD at 1.1450 and close it at EURUSD 1.1500 and i make 500 USD profit, so who loosed this 500 USD? Like in money changer they bought in USD notes for exchange and make profit from the spread. They will sell USD notes as long as they can make profit base on current exchange rate. What happen if the USD become weaker? I believe no one is willing to loose money doing business and they can just put up a sign board telling that they are running out of USD notes or they can maintain their exchange rate but no want will buy from him. No matter how they still can prevent their losses and selling again USD notes when the exchange rate bounce back. I am referring to true ECN account where the trade is link to the banker or instituitional liquidity provider. I dont think they want to loose money either. So again my question if i make profit in forex trading, who loose? Sorry for my bad english if you could not understand my question. I really need to find out this before decide to go further in this forex trading. I started trading forex two months ago and still a newbie in the learning stage. So far had loosed few thousand USD but i still see a potential to make money from forex.