I am 18 years old girl and i want to tighten up my vaginal walls, how can i do it naturally?

I am 18 years old girl. i had sex first time when i was 16. its been two years now that I've been hahaving intercourse with my boyfriend. it happens almost once in a month. But now my vagina is kind of loose. like not really loose, but yes. And its not that pleasuring as before. I want to ask that how can i tighten it yp? its been a month that we're not doing it as i want to tighten it up. and I've heard that if we don't do it for 6 months, it will be tight like before. can anyone help me?
how can i naturally tight it?
i am really tensed because my family wants me to marry rhis other guy and i cant marry anyone else because then he will know that I've been doing it before which is a huge cause of shame.
please help me