Seikimatsu★Darling(1992)

Meet Ogata Kohsaku, your average hot-and-cocky het boy, who falls head over heels in love (as he's prone to doing), except this time the object of his affection happens to be MALE. Enter Takasugi Yoichiroh, who (yaoi manga being what it is) of course reciprocates Ogata's feelings. All would be happy and fuzzy and resolved in one chapter, except for the fact that Takasugi isn't any more eager to be on bottom than Ogata is. Far from it! In fact he has everything in mind for Ogata that Ogata had planned for him... And that scares the bejeezus out of our mostly-hetero hero.