You are so young and your boyfriend is going into the military. He may change, A LOT, after that. And because you are sooo young, you too will change.
You might not even be compatible then.
Do you really want to get married and then right away be separated?
That can totally ruin a marriage.
You need to think things through.
As for your question, I don't think you can stay on your parents plan when you are 18 and married. You would be under your husband's plan. As soon as you marry, you are now a different household, a separate family from your parents.
But there are some companies that may do it differently, so you have to ask the one your parents are with directly.
Don't think that you can just pretend and everything will work out - like living at home so that you can be under the plan, because they will find out that you got married sooner or later, and if they do not cover you under your parents plan, yet they pay out claims because you didn't tell them you got married, you will put your parents in a very bad situation where they may be charged with fraud, and you also.