
I don’t think it was explained clearly or I somehow missed it but during jeremy’s trial, shuli tried to annul her marriage in order to save jeremy and it is later said that she exposed the bedroom matters in order to save him so what exactly did she expose and on what basis did she try to annul the marriage? Did the late marquis marry her in name only and didn’t touch her in order to have her as the head of the household after his death?

Shuri tried to annul her marriage to the late Marquis of Neuschwanstein, Johannes, by bringing to light that:
1. she and Johannes never consummated their marriage
2. Johannes never had the intention to fulfill his marital duties or have children with her.
Basically she's trying to prove (with Johannes' letter and the Count's testimony) that she is still a virgin after marriage cause Johannes goal wasn't to have her give him more kids, and so she can use that as a legitimate reason to dissolve her marriage. If it is accepted, Jeremy is the next Neuschwanstein head by default, will not lose his hand, and can demand a duel of honor to defend the Neuschwanstein family honor. In the context of the story, a legitimate marriage is when a husband and wife have fulfilled their marital duties with the intention to have kids. And yes, you are correct- Johannes only married Shuri to protect his kids and the Neuschwanstein name/marquisate/wealth/power until Jeremy can inherit.

just making sure before reading because of the cover, is this a love triangle?

FL is villainous here so she uses her sex appeal to lead on men and get revenge, not really super focused on the "love triangle". FL is not really "pure" so she has no qualms using her feminine wiles haha
Spoiler
2nd ML doesnt really act on his feelings for her so thats where he lost against the 1st ML. 1st ML knows about her villainous side and accepts it while 2nd ML doesnt know she's wicked.
Did jeremy just admit he has feelings for shuri and is only pretending so she doesn’t get hurt????? Someone please tell that’s not it( T﹏T )
ya, it’s also implied jeremy has feelings for shuri in their past life as well.
It seems like it’s a little more complicated than that. The attachment he has to her goes deep, and his understanding of his position means that even if she is the only one he is willing to open up his heart to and love (in general, including romantically), he will never show signs of attraction for her. Maybe if she felt something for him, he could get into this taboo incestuous relationship, but then again, this is exactly what Nora and Jeremy talked about, and it’s something that even Jeremy himself seemed to be disgusted by while being accused of it and also when he reprimanded Elias (In their first lives, we only saw his special attachment to Shuri from Ohara’s perspective, so it is difficult to tell if he had that kind of romantic feelings for her even tho they were not in a good light with each other’s.)
Just my interpretation (〜 ̄△ ̄)〜
Is it completed?