I mean...where's the NTR here? Haru has emotionally and sexually already chosen Ria, if Suzuka wants to go to this other guy, either for comfort or for some sort of scheme to win Haru back over then it's going to fail regardless of the reason.
If Ria catches Suzuka with this other guy, she's just going to use that to fully pull Haru closer to her and if Haru catches Suzuka with this other guy then he's just going to run to Ria for comfort.
The only winning move for Suzuka is to just move on from Haru.