Jounetsu no Wasuregatami

Sabine doesn't know what to do when Gavin, the millionaire she broke up with a few years ago, suddenly appears before her. He's found out that she secretly had his son three years ago and has been raising him on her own. But when Sabine refuses to let her son be taken away, Gavin asks for her hand in marriage instead! Sabine is hesitant, but she finds her resolve slowly breaking down as she witnesses how he cares for her son... (Source: Renta!)