A high court misdemeanor carries a penalty of up to 2 years of prison. So even though it is called a misdemeanor, he has much of the same consequences as a felony. Unless the prosecutor is willing to agree to probation or some other non-incarceratory sentence, this would not appear to be the world's most generous plea.
On the other hand, even if this is an open plea, meaning the sentence would be up to the judge, it can be no worse than 2 years in prison. So your boyfriend needs to sit down with his lawyer and fiind out, first of all, what his maximum risk is if he goes to trial and is convicted of the top count. Then he needs to learn the strengths and weaknesses of his case as a trial case and get his lawyer's opinion on the odds that he will be acquitted after trial. Once he has all of that, he can weigh the offer against the possibility he will be convicted at trial and choose the one he can best live with.
This particular decision -- choosing between two very unattractive alternatives -- is the most difficult type of a decision any individual has to make. I can't tell him what to do. I am not his lawyer and don't have enough knowledge of the case to advise him. But I can tell him what he needs to learn from his attorney.
Once he makes his decision, even if his lawyer disagrees with it, his lawyer is professionaly obligated to give him the best possible defense he can manage.