Imagine Ikejiri being Daichi's first love but Daichi decided to break up before they got to different high school because he thought he could not stand not seeing the other as often as he did at that time and didn't want to screw everything up if he was going to meet someone who'll make him feel the same way he felt for Ikejiri - because he knew that breaking up would be terrible, but guessed that being cheated on could be even worse
The following year he met Suga and at some point (when they got together) he thought that maybe the breaking up with Ikejiri had been the best thing to do because he can't see a way he would have resisted Suga
When he meets Ikejiri again, he can't help feeling a lot horrible and he kinda hopes it's not because he stills loves him (well, deep inside he knows he still loves him because first love and all, and the breaking up has never been because they didn't love each other). They talk that over and Ikejiri tells him he understands and that there's no need to feel as bad as Daichi feels because the point of their separation was exactly to avoid a hard situation and this has perfectly worked.
(Daichi later tells everything about their relationship to Suga because he feels like he should tell him - Suga doesn't really see why but he still hugs Daichi and pat his back gently to comfort him)