Don't keep girls just because "they can give you more girls". That puts you in a needy position, which is the wrong frame. Besides, it's not a good idea to date a girl's friends. That will only mess things up and cause drama.
About your friend and his lack of gratitude... This should be a lesson for life to you. Never expect any gratitude from anyone! Ever! You will not get it. By giving things and doing nice things for your friends, you put them in
debt - they owe you something. On the other hand, if you do something bad instead, they will indeed get revenge, since that is a
pleasure. (I took this from the book The 48 Laws of Power by Robert Greene by the way). Be generous, give things, but never expect anything in return. In fact, you can never trust a friend. But you can indeed trust an enemy.
My advice to you is to ditch that girl and get over it. Don't rely on wingmen. Any other man, friend or not, is always a competitor. Go out and meet women alone instead. That is what I used to do.
Here is a documetary about alpha males (humans compared to apes). It is very interesting indeed and can give you some insight in human behavior:
https://www.youtube.com/watch?v=_TijDInhnEg