I don't expect Maruto to go this route, but the two I can think of off the top of my head go something like:
The nihilist toxic nobody learned anything path:
He's back to a similar circumstance as the first go around: He took a chance to get with Hikari with the confession and it didn't work out well, Aya is throwing herself at him, and Hikari seems to be tacitly condoning, if not encouraging, it. So Yuu again thinks it's hopeless with Hikari and takes the kinda cowardly route of trying again with Aya 'cause after all he thinks he was starting to fall for Aya and with Hikari's help they seem to be on the path to clearing the air about their communication issues that crashed their first ship. I also think this is the sorta thing that's doomed to fail b/c Hikari can't keep them from falling back into their bad patterns.
The uno reverse path:
He's confusing loving Hikari as a friend with being in love with her, because he's been in love w/ Hikari for so long that he wouldn't recognize that he fell out of love. He confessed to Hikari after meeting w/ Aya to lock in the safe stable comfortable relationship instead of risking the one he now really wants.