I think it's pointless to debate whether Lewis had chemistry with Charlotte or not, because Cleo is the love of his life, and his relationship with Charlotte literally happened because he had to do something to prevent Charlotte from seeing Cleo as a mermaid in 2x10, and so he kissed her. Furthermore, despite the fact that they were both brilliant and scientifically-inclined (although Charlotte was also artistically-inclined), they were utterly incompatible. Charlotte was unaware of all of Lewis' interests, and she made no effort to engage in them (as evidenced by the birthday party she threw for him, which ultimately became about she wanted than about what he wanted).

Also, Charlotte was the aggressor in the relationship and relentlessly pursued Lewis, while he was still head over heels in love with Cleo and was just never going to be over her. Charlotte and Lewis' relationship was not just unhealthy and unbalanced, but also destined to fail. I do believe however that the relationship had to happen, because it was really vital to Cleo and Lewis's love story and growth. While the narrative spent an exhausting amount of time on Charlotte/Lewis, I think the way in which Clewis developed in season 2 so that they could come back together stronger than ever was beautiful and amazing, and Charlotte and Lewis's relationship was important to that fact. But on its own, Charlotte/Lewis was a horrible relationship.

It would have never worked cause he loved Cleo to much