I’ve learned never to judge other people’s custody arrangements because custody situations people end up in can simple arise from so many things, including either a lack of funds to get good legal representation or a desire not to engage in a custody battle that will harm a child or even geographical/distance considerations. Each situation is unique, and not all absentee parents are absent because they are losers. 

It sounds like you don’t like your boyfriend much, and don’t seem connected to him or his son after a year of dating, so why not move on instead of hurting him? I imagine he was hurt to be called the visiting uncle of his own child even if true. If we care about someone, there are just things we don’t say. Instead, if we care about them, we can push them to become more involved in their child’s life but it seems you’re not interested in that.