Lie to your parents, set up a time and place, and just enjoy yourselves. You’re 18. They can’t legally forbid you from having sex. You’re an adult in the eyes of the law. I get that you still want to be respectful of their wishes, but there comes a time in your life where you have to start making decisions for yourself. This is one of them.
If you want your boyfriend, have him. Make it happen. Don’t let your parents stop you. There’s always a way. It’s not about what THEY want, it’s about what YOU want, and you have every right to make this decision for yourself.