I'd recommend most of the VNs made by Holicworks, Shingakkou Noli Me Tangere, Haiiro no Arcadia and Bewitching Sinners (MC is gender of choice but it only has male LIs). And I guess Dramatical Murder wouldn't be that bad of a choice either if you didn't play it already.
Have you looked for it on the scenes gallery ? I think you should play the scene that has this CG directly from there. I think that's how I unlocked it.
Finished Hozumi's good ending route from Suito wa Hakumei. The romance was much better than in his normal ending route but it only started towards the end of his route and thus there wasn't much of it. Also the plot of his route really sucked. The main villain of his route was an irrelevant NPC...
I found Asuma's (the redhead) route pretty boring overall but I did like Shirasu's, tho a certain plot point in his route did disappoint me. I haven't played the other 2 routes yet but I do plan to play Taiga's as well eventually.
Maybe Kintouka even tho I haven't even finished a single route from it lmao (I dropped both of the routes from this VN I've played with one single choice left till the end in both of them). I think the longest BL VN I've finished a route from is Shingakkou Noli Me Tangere, tho most Holicworks...
Favorite: "Bad boys" types who end up becoming whipped for the protagonist (however they can't hurt the protagonist too much before that happens). Least favorite: Any r*pe dynamics, even if it's the romanticized one where the uke is secretly into it/ends up liking it by the end. (I can tolerate...