To be fair, we don't have much of a reason to not believe him. At the opening it's pretty clear that Josuke has lady friends lined up who would gladly… up, pat his pompadour, if you catch my drift.

However, we're given no indication that he's taken advantage of that. In fact, every indication seems to be that Josuke's a pretty upstanding guy, loves his mom, etc. And Hell, it isn't hard to imagine why Josuke might be more into 'pure love' than anything: guy has a deadbeat dad.

Speaking as someone who's father, let's just say, decided to not stick around, yeah, growing up watching your mother either be alone or drift through other potential suitors who may come, stay or go does end up nawin' at ya. It does make you appreciate the idea that maybe love should be, and could be, something more than what you grew up with.

Some people go cynical. Some people, like Josuke, go optimistic.

Add to that the fact that his father figure was his gramps, a policeman you can reasonably assume his moral compass is pretty well adjusted. Even his money making schemes are thought up in such ways that they remain victimless.