We appreciate the sensitive nature of this question.

In order to remove your niddah status, you would have to observe the five-day wait followed by seven clean days and immersion, as a married woman does.

However, you should know that this does not remove all halachic barriers to having relations. There is a decree against single women immersing in a mikveh in order to deter couples from having relations outside of the context of marriage. Additionally, a man and woman are not permitted to be secluded together (yichud) as a matter of rabbinic law, even if both are single and she is not in niddah.

According to many halachic authorities, including Rambam, having relations outside of the context of marriage violates a Torah-level prohibition.

It can be very difficult, especially for a sexually experienced couple, to have a committed relationship without relations. Observing the laws of niddah does address the punishment of karet. However, marriage is the only type of commitment that halacha recognizes as a permissible framework for relations.

Please let us know if you have any follow up questions.