The other electron comes in, absorbs that photon string, and moves off. So, later, we see this electron string moving this way, and this electron string moving this way. They've exchanged a photon string. The distinction between matter and forces is somewhat artificial. You see that is all the same string, the same kind of string, just that this is a particular excitation which we could identify with an electron perhaps, or in some other experiment, with a quark.
General relativity explains that light is bent by mass.
One of the consequences of the theory is that one is forced to the conclusion that, in a fundamental sense, these strings live not in the three spatial dimensions that we observe, but in nine spatial dimensions. Now, one must remember that after Einstein proposed his theory of general relativity, namely that gravity is the dynamics of space and time, it was realized that the number of dimensions in the world might therefore be different than the three that we obviously observe, namely, that way, that way, and that way. There might be extra dimensions if they were small, and compact, and curled up. Imagine six-dimensional balls attached to every point in space. That is always a possibility in any theory which contains gravity.