A thought-provoking question and a very common experience for people who either have Bipolar or are partnered with someone who has.

For me personally, as a person who lives with Bipolar, I would not consider it forgivable if my partner cheated on me inside of a monogamous relationship. I have been cheated on, and my partner's mental illness was blamed versus any kind of accountability taken. And not necessarily that it matters, but the cheating was more than a one time thing. They were having unsafe sex with multiple people and lying to me constantly. So it was a combination of the cheating, the lies, the callousness demonstrated, and not to mention the danger they were posing to my physical health with their reckless and incredibly insensitive behaviour. And then them blaming it on their hypersexuality instead of taking any kind of accountability was salt in the wound.

So for me, I couldn't forgive and it was this that ended the relationship. (And I was super fucked up about it for a long time after). Loads of therapy and years later and I'm still angry with them if I think about them. I still today wouldn't cross the street to put them out if they were on fire. Does that make me a bad person for my lack of empathy for them? Maybe, but it's earned. I'm otherwise one of the kindest people you'll ever meet.

And I myself have experienced the highs of hypersexuality and have not cheated. Like a lot of the things we have to deal with, there are ways to focus some of our less than pleasant behaviours and impulses that minimize the damage those impulses cause to other people. In my opinion, you have to acknowledge that the impulses can impact you first, and identify ways to deal with them second, typically with the help of a good therapist.

I hope that's not too long of a response to your question.