My own scan from Only The Ring Finger Knows Novel 2: The Left Hand Dreams of Him.

Book Description:
Yuichi, who has just been accepted into an extremely prestigious national university, has planned a vacation for his exam-ridden boyfriend, Wataru. Looking to raise money for the trip, Yuichi agrees to a short-term job with his college senior Asaka, whose cool attitude and mature personality makes for an uncanny resemblance to Yuichi himself. Taking a liking to Wataru, Asaka makes no effort to hide his interest and advances. How long will Yuichi be able to contain his frustration and jealousy?!

The vector art is available here:

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