Road trip rudeness

Hi! I’ve been struggling recently with one of my friends being rude and negative. We are on a road trip together and I have few opportunities to be apart from them. I’ve been trying to have compassion and empathy and not let their bad moods get me down. It’s been going pretty well, but their negativity is constant, so i’m feeling like i’m fighting this uphill battle, because i have very little time to process my emotions and choose to respond with love before the next put down. I’m feeling like I’m managing well through out the day but at night i feel so tired and sad. I think i am repressing my sadness rather than properly forgiving my friend. I’m not sure where i’m going wrong. Do i need to set a boundary? Thanks 🙂