What emotions is Romeo having during this monologue?

As much as there is remorse... there is also love. He's looking at Juliet, at how beautiful she still is...even in death. He marvels at how death has not conquered her fairness, and I suspect he means more than simply outer beauty. The love of his life, his wife, is dead, and he is probably feeling a little shock, the grief may not have fully set in. He decides that death is his only way out of the pain of living without her, and thus takes his own life. So the underlying grief must be immeasurable! Most of all, don't "act" the emotions. Just allow yourself to feel them.