Based on this chapter, there's several possibilities i could think of :
1. Itsuka might have the ability to rewind time.
2. If one was true, then he most likely using that on himself everytime he started to grows feeling for shaayu. Basically everytime there is a moment that makes his feelings grow, he reverts to a few minutes before this happened, to make his feelings gone.
3. If number two is true, and based on his conversation with demon lord a few chapters back, the reason why he reverts time is because he feels he doesn't need to have those feelings. Here, he said that heroes supposed to be equals , and not to have feelings for a spesifics person. So it might be possible that itsuka is also "the Hero" just like shaayu. I think he also one of homonculus, created by the empire or something to fight the demon king. However, unlike shaayu who got her gene from demon king himself, he's created from a different source. If this true, He most likely created before shaayu is created, maybe something like an early prototype, and shaayu is like the succesful product.
4. Since itsuka seems like he understand a lot about these Hero homonculus circumstances, he might be homonculus himself, or someone who involved in the creation of the homonculus. He also seems stronger than it looks, if my hypothesis from number 1 it's true.