Hmmm... I don't know much about guinea pigs, but I do know a fair amount about rabbits, and I agree with what everyone here has said so far.
It is clear that a rabbit and a guinea pig living together is not a good idea. However, you could possibly risk letting them have supervised playtime together. Many species get along well if they don't have to spend all their time together.
Even if you get another rabbit, there is no guarantee that they will be able to stay together in the same cage. And Rabbits are territorial, so if they feel that their space is being invaded, they will lash out and try to establish dominance in any way possible.