León to San Martín del Camino by bus with
www.alsa.es/en
San Martín del Camino to Astorga by bus with Alsa
Astorga to Foncebadón buses are operated by
http://autocarespedrin.e.telefonica.net/servicios.html I don't think they run them daily (in fact, I think it won't be service most days of the week) but I'm just guessing so I could be wrong. They don't show schedules on their web so you would need to phone them to know days of operation. If the bus schedule doesn't suit you, your best bet would be to go all the way to Ponferrada (either by train with
www.renfe.com or by bus with Alsa) and wait you walking companion there (to sleep at diferent locations one night wouldn't be a big problem, would it?).
Foncebadón to Ponferrada I don't think there are buses on this route so you would need to call a taxi (if you didn't decide to go all the way from Astorga to Ponferrada).
Ponferrada to Villafranca del Bierzo by bus with
www.alsa.es/en
Villafranca del Bierzo to O Cebreiro. Take a bus from Villafranca del Bierzo to Pedrafita do Cebreiro (roughly 4 or 5 kms away from O Cebreiro) with Alsa. The bus from Pedrafita do Cebreiro to O Cebreiro (operated by
www.monbus.es) departs early in the morning (and doesn't run on Sundays) so you'll probably have to take a taxi for that short route.
O Cebreiro to Triacastela by bus with
www.monbus.es (no service on Sundays)
Triacastela to Sarria by bus with Monbus (no service on Sundays)
Sarria to Portomarín by bus with
www.empresaportomarin.com
Portomarín to Palas de Rei I don't think there's bus service (but check locally just in case) so taxi would be.
Palas de Rei to Arzúa by bus with
www.empresafreire.com
Arzúa to O Pedrouzo by bus with Empresa Freire
O Pedrouzo to Santiago de Compostela by bus with Empresa Freire