@Daisyvodka hello, what do you mean by not very bright? I assume just not sharp but not disabled.
Every person on the planet lacks awareness about things they do. It's never a free pass. It doesn't matter if they plot to manipulate or do it because it's a habit and that's all they know. They are responsible for their actions.
You don't have to logically decide if they are being genuine or not. Trust your gut and what you expect from a relationship. People with below average intelligence aren't automatically dicks. The fact that you are asking the question makes me think you don't trust it's genuine.
And it probably isn't. True awareness often leads to changed behaviour. If it doesn't then maybe there is trauma and a psychologist might help. That's still not your responsibility. Working through deep rooted issues is no walk in the park. Highly intelligent people take years to do that. It takes a willingness to truly change and commit to the change. Many people start by reading books or watching tiktoks, but ultimately a person has to start somewhere and if there is no start, just promises, that wouldn't be good enough for me. You get a chance and maybe another but then that would be it.