Does sex ruin a high school relationship even if you've been together for over a year and really love them?

Me and my boyfriend have been together for a year and a half and we decided we want to have sex but we've heard in sex ed that sex can ruin a relationship and we don't want to ruin ours. Will it ruin our relationship even if we care deeply about eachother and know eachother better then anyone else?
Does sex ruin a high school relationship even if you've been together for over a year and really love them?
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