Background Check | Ghosted Previous Employer

I'm a junior about to go through my background check for my SA internship this summer. It's at a decent-sized MM firm on the west coast. They've recently asked for references for my background check and there's one internship which I'm worried about. It was a small startup with one person, and I ended up ghosting them at the start of last December. It's a long story about why it happened but I fully regret doing this. It's been one of my worst lapses of judgment. What can I do about it now? If I list him as a reference I know he won't have good things to say about me even though I did well the entire internship. What should I tell HR if they reach out about it?