Should I tell my mom?

Ok I’m 14 and secretly dating a senior from a different town... so we have been sneaking out at night to see each other and things have been happening... he understands I’m not ready for sex Bc I want to be 100% sure but we still ummm mess around😂🙃 but

today my mom told me she wants an open relationship with me especially at this age meaning letting her know my plans of when / if I have sex , have a bf, have my first kiss, etc and I want to tell her but I’m scared she’ll freak