Amethyst no Yuuutsu

Aiji Ubukata is a highly qualified government ambassador who has almost no relationship experience. After finally being freed from the celibate lifestyle of an extended overseas position in Saudi Arabia, he realizes that even a glimpse of a woman's skin arouses him. Crammed into a crowded train on his return from the airport, he saves a beautiful man, Akira Shimizu, from a molester. As Akira turns to thank him, he spies Aiji's raging hard-on from their close contact...!! "I'm used to this kind of thing. Just leave everything to me..." When Akira brings Aiji to a hotel and makes him cum instantly with a blowjob, Aiji can't help but fall in love with him. However, Akira has lived his whole life pursuing purely casual relationships without opening himself up to anyone, so the idea of a relaxed date with Aiji doesn't exactly appeal to him. When Aiji asks Akira to think about a serious relationship, he dodges the subject and asks him to another hotel instead!

(Source: Shinkosha)