My boyfriend has an unhealthy obsession with monkeys

I’m writing this post because he just told me to refer to him as “The Monkey King”. he is seriously obsessed with monkeys, the other night i woke up to him gripping his phone with his feet and calling it monkey practice. he’s started laughing like a monkey too, and sometimes i see him just staring at monkeys laughing. his youtube feed is filled with monkeys. he goes to the park and swings from the trees like a monkey and climbing them. He tries to use his feet as hands whenever possible, even when we’re in public. I have no problem with his love for monkeys aside from the fact that it has now gone to the point that other people ask me if he’s mentally ill. he keeps insisting this is normal, but I don’t think it’s just a hobby anymore now that he’s literally fantasizing about becoming a monkey. Should I break up with him or just tolerate this strange obsession ?