I think that each statement has a different answer. The first is that the ending of the drama shows that Jimmy and Alison are made for each other. Both of them end up recognizing the reality that they shared was a real one. It was filled with hurt, moments of joy, and a sense of the real that Jimmy sought to validate through his being and one that Alison learned to embrace in hers. In Act III, Alison recognizes that she does not want to be in Jimmy's way if he is happy with Helena. It is to this point where Jimmy recognizes that Alison is a part of his identity: "I may be a lost cause, but I thought if you loved me, it needn't matter." In their reconciliation at the end with the bear and squirrel game, it does seem that they have recognized how they need one another and how they are made for one another.
The second half of the equation is a bit more nuanced. There might be no other solution other than the reconciliation experienced at the end of the drama. There is no solution for them in a world outside of their own experience. Jimmy is not able to find that emotional level of being "real" and authentic with Helena. He recognizes at the end of the drama that it is only with Alison that he shares this. Alison recognizes that there can be no solution for her, in general. She lives with the loss of the baby, and that she was not able to "protect her unborn child." In both of their conditions, there is no solution for either of them outside of taking refuge in one another. It might be for this reason that the ending of the drama is so poignant. In the end, both of them might be failures, but in the eyes of the other, they are a success. Thus, there is no solution for either of them outside of one another, which is their only haven in a heartless world.