I don't have similar stories but since no one else has replied...
You are saying all the right things. It is very important that your boyfriend not lie, as once an immigration official thinks someone's misled them, that's a much worse position than just telling the truth in the first place. The more evidence (on paper) he brings with him of his ties to the U.S. and plans to return there, the better his chances. Obviously a return flight is a must. Having an itinerary should also help (that is, he can say where he plans to visit, what sights you are going to see, etc.)
It is also evident that you both understand the rules and plan to abide by them. This can help, as if an immigration official questions him about his plans (marriage, etc.) he can explain what you plan to do and that it is legal. In other words, you know the rules.
Unfortunately, it's not possible to say with 100% certainty that he will get the visa he wants on the day. But the more upfront he is and prepared to show evidence if required by the immigration officer, the better his chances.
Good luck.