I see nothing that indicates more than biochemistry and experience and individual variation is required to "explain" love. Remember that "purely physical" includes information encoded into the brain either during its construction or later; that's how learning works, that's how thoughts work, that's how emotions work.
If you want to argue that love is operating in software/wetware that may be true, but those processes are running on a physical brain and body. We don't get metaphysical about our spreadsheets even though they too are software; we accept that they are supported by physical mechanisms.
True, we do not fully understand the operation of the brain yet. But we know enough to know that we are animals, that the difference between us and other animals is more a difference in degree than in kind, and to observe changes that happen in the brain as we learn and in response to stimuli. Guessing at something which we can't define to fill a gap where we don't yet know all the details strikes me as an unjustified leap of faith.
Sensation can be explained as nothing more than the body doing what it is designed to do. Clinical depression can be explained as biochemistry not doing what it was designed to do. What makes love different than those?