To have compassion for a character is no different from having compassion for another human being.
AU: when Loki let go of the staff, he fell onto Earth. On Earth he met some new friends, and the new experience of friendship had softened his anger and healed his broken heart (a bit). They were hanging out one night, and when they talked about stars and universe, he missed his brother, and his home. And Thor was so pleased to know.