If I’m not nida can I be with a man ? Is there a heter?
There is no heter. Not only is it not permitted to be with a man, there is also an issur “yichud” (seclusion) for a single girl to be alone with a man.
Rambam & Raavad Ishus1:4, Sanhedrin 21b, Rambam Isurey Biyoh 22:1, E:H 22:2