If I may add some information to what you've just written...
A visa (issued by the U.S. Dept. of State) is merely an authorization to show up / present yourself in front of a U.S. Immigration Officer (the CBP Officer – U.S. Dept. of Homeland Security) at a U.S. POE ("Point Of Entry") – might it be an airport or a land border POE.
The duration of the visa means that you can use (meaning to show up at a POE) at any time until its expiration. You can technically use it to present yourself at a POE on the very last day. For a B1/B2, it is generally 10 years.
The maximum duration allowed for your stay (as stamped on the passport) is left at the discretion of the CBP Officer, and ultimately decided upon entry (regardless of whether a visa mentions a maximum duration annoted as a remark by the Consular Agent who issued the visa – in the comments section). On the vast majority of the cases, people on a B1/B2 visa are granted a maximum stay of 6 months. This does not mean however that the visitor should stay that long, except for valid and legitimate reasons (how can a visitor indeed stay that long – this would demonstrate no ties in the home country, no job to go back to, and a stronger suspicion of immigrant intent).
In the case of OP @MLo, if your fiance intends to come back regularly to visit you on his B1/B2 visa while the I-130 and CR1 visa and processed, it would be wise to not stay up to full duration of 6 months, because it may potentially jeopardize the subsequent B1/B2 visits and bring suspicions upon himself.
I would advise 3-4 months, which should be enough for the wedding, spend quality time / honeymoon etc... assuming your fiance can take that much vacation and demonstrate he has the sufficient financial means.
Again, do not volunteer to provide more information than what the CBP Officer asks you. However, if asked how long he plans to stay, do not lie: be honest, factual, assertive with proof to back your plans (return ticket, events agenda, bank account balance etc...).
Stating that you are coming to the U.S. to marry a U.S. citizen will almost always bring scrutiny and unless the CBP Officer is easy that day, your fiance most likely will get additional questions. He needs to be prepared and convincing.
Good luck