Do you mean TCD MATZ?

On a scale of 1 to 10, Hongjoong is an 11 😂. Although, I would argue that he’s actually more possessive than he is jealous. He can’t stand anyone else touching Seonghwa. He’s more okay with people looking at him so long as he’s wearing something that shows he doesn’t belong to anyone else but him (like the outfits with the armband specifically made to be used as a thigh garter on Seonghwa). Hongjoong’s jealousy manifests with being petty and the need to reaffirm Seonghwa is his and his only. This will typically show with Hongjoong being a little rougher during sex (more marks, and a tiny bit more degradation), and afterwards he’ll spoil Seonghwa rotten with flowers and presents, things he can show off. 🙂‍↕️ Depending on Hongjoong’s mood, he’ll take Seonghwa with him everywhere until the green beast in his chest settles down.

We have seen a bit of Seonghwa’s jealousy in Borrowed Time, but it was nothing compared to the way he’ll react when he is confident about where he stands in his relationship with Hongjoong (aka when he knows Hongjoong loves him and will just about bring the world to Seonghwa’s feet if he asked him to). I would say that Seonghwa is as jealous as Hongjoong is, and he will give Hongjoong the silent treatment until Hongjoong worships him (that only happens when Hongjoong doesn’t notice Seonghwa’s jealousy and doesn’t do anything to soothe him on the spot). Ways that Seonghwa might do out of jealousy would be something Hongjoong taught him in Borrowed time, which is watch the person dead in the eyes while kissing Hongjoong or touching him in a way that will show Hongjoong is Seonghwa’s just as much as Seonghwa is his. Very rarely, but it can happen, Hongjoong will let Seonghwa take control during sex if he sees that’s what Seonghwa need to be soothed. 🙂‍↕️

None of that are healthy coping mechanisms, but MATZ isn’t in an healthy relationship in TCD (well, it’s actually very healthy FOR them, but not to outsiders 😏)