So long as he is not attempting to have visitation then you shouldn't have to worry about it. However, if he is wanting visitation, you should be able to file a petition in the juvenile court in your county to have him either barred from visitation. It's possible he might also get visitation but with supervision. You should talk to an attorney in your area to assist you with filing that petition.
Nothing in this answer creates a attorney-client relationship nor is it to be considered legal advice that can be relied upon without more information.
If you are not interested in getting child support or establishing paternity, right now that is your choice. As the other attorney has responded, if the putative (fancy legal term for likely biological father) files a petition in child support or Juvenile court, you will have to deal with the issue then. Juvenile Court Judges will not be happy to know this man is a sex offender, so you should get prepared and get copies of documentation showing that this man is a sex offender and put that in a file somewhere. If he files for visitation, you should hire an attorney. If you get married to your current boyfriend, then down the line he could file for a stepparent adoption and terminate the putative father's legal rights.
This answer is for informational purposes only and is not to be construed as legal advice.