Um...He literally cheated on Lena with a hot model that he was hired as a photographer for. After cheating on her enough times, he decided to nudge the knife deeper by getting Lena into threesomes.
The rule of thumb is: if he cheated on you once, he'll cheat on you again. And the fact that Axel makes moves on Cindy despite Lena having sex with him and 'reconnecting'...Well. It doesn't sound like he actually intends on being a good partner to her.
And yes, yes...ik. They're not together anymore. But if he planned to get back together with Lena, why is he screwing around with someone else? Not exactly helping his case. Not to mention he's an example of actual "toxic masculinity" that people sometimes throw around. As in, an actual clear cut example of it. Jeremy might be a sleazy, cocky cockroach, but at least he's not a controlling or toxic freak about it, just like Ian.