My ex wants to prevent my boyfriend from being around our son but if I marry the boyfriend can he still try this?

First, your ex-husband can file a motion or petition with the court to request anything he wants. Of course, if he files a frivolous motion he won't succeed, but that doesn't mean he cannot try. Second, regardless of whether you marry your boyfriend or not, unless your ex-husband can demonstrate by a preponderance of the evidence that your boyfriend poses a threat of harm to the child, he cannot prevail on a motion or petition to keep him from having contact with your son and developing a step parent relationship with him. Marrying your boyfriend only makes it harder to prevail on a motion or petition, but never makes it impossible. The question is not whether marriage can prevent your husband from filing, the question is whether your boyfriend/husband poses a serious danger to your child.

It depends on the reason why he doesn't want him around. If it is to protect your child, then sure, he can continue to ask. If it is because of the immorality of your situation, I am inclined to say it is none of his.

The short answer is "NO"; but former husband may still harass you by filing with a Judge for a decision.

Cannot stop ex-husband from filing, but based on what you say, ex-husband should not be successful.

Not necessarily will marriage make him stop. Consult with an attorney.

Without a criminal or domestic violence background, the court will not dictate who can be around your son. If marriage is contemplated be sure you know all of his background so that you do not find yourself without custody due to his past.

Wrong, sorry. The judge won't order your new boyfriend away from the child just because your ex doesn't like him, but if there are reasons why the judge thinks it's in the child's interest to be kept away from your new boyfriend, marrying him won't cure those reasons and could even cost you custody of the child. If that's your reason for getting married, you should wait till you have a better reason. That's my take based on the little information you've given, but if you have a lawyer get your advice from him or her and follow it.