Kitto, Shiawase na Ketsumatsu

From Chrima Scans:
Having barely escaped being killed before birth by his parents, he thinks he’s used up a lifetime worth of good luck...
Sumire, a bartender who attracts only good-for-nothing men, has given up on happiness.
Estranged from his parents, he should have gotten used to being alone...
But a distant relative who’s a university student, Yuushin, comes to spend some time with him, and Yuushin’s feelings for Sumire grow stronger and stronger...
A heartrending age-gap romance.