Upvote:2
Telling the truth is the way to get more probabilities to get the visa. I interpret this in a wide sense, so also not hiding important informations.
Why are you travelling in USA? In specific locations? Alone? Officers checks such facts and get an idea of what you will do, and the risk. There is no wrong way to answer them, but you officers should be convinced that you are telling the truth, so consistent answers, and with some reasoning. By hiding information, you will probably tend to hide other facts, and officer could notice and so have doubt of your real application purpose.
For the real answer: it is difficult to tell you. It depends on too much facts (and training/experience of officer, which we don't have).
If your boyfriend will be deployed soon again outside US, you will have good reason not to remain in US.
If you both plan to eventually marry, you may also get more probabilities: you will (probably) not ruin your chances to live in US with an overstay. You can also explicitly say that if you marry him, you will seek legally to stay in US. They will not decide now for such plan, just for your short term plan (and so that now you will not overstay or work in US). Telling about long term plans could make more easy to understand what you will do and will not do on short term.
So don't hide your relationship (and so the reason you travel in US). Telling them should only help you. But you may still get a refusal, but in my opinion, because other reasons. Check this site, and tell your boyfriend to read your application, so that you will not make newbies errors (like missing documents, or assuming US officer will understand your culture/lifestyle/school system/job/...).