Relationship Advice

I currently been in a relationship for 3 years am 21 and my partner is 25. I never had sex ( am a virgin) but now that i been with my partner I sometimes think about having sex with him but even when we cuddle I get so nervous. We have a kid in our relationship due to his past life when am with his kid I feel like am ready but am just afraid that he might leave me after sex. What should I do?