Would you contribute to a collective betting between you are your friend? Collective betting is a real thing, people are joining staking power with one another to place bet.
Yeah it makes some sense in that it's basically like sharing your risk with the other party with the catch that you also gave to share profit. However you have to consider something too, which is in gambling most times your Risk is directly proportional to your reward in that case it's almost same thing as one party taking half the risk alone.
Aside from this it may not be very convenient with online gambling probably in a case where that particular stuff goes against the terms of usage of that particular casino.