Prequel to Gravity Eyes
Long-time lovers and heirs to rival yakuza groups hit rough waters when one agrees to marriage and the other is pursued by the puppy-like host Kyoya (who will get his own happy ending in Gravity Eyes). Injured over his lover's seeming infidelity, Homura temporarily dates the sweetly persistent Kyoya -- something that set the comments section aflame. I thought it was a totally reasonable move by someone who is heartbroken and devastated, but then I've been heartbroken and devastated. If I'd read this while younger, I might have been mad too.
Tsumasaki ni Kiss