The percentage of high school relationships that last varies depending on the source. Here are some statistics from the search results:

• 63% of high schoolers have been on at least one date before they reach 12th grade.
• 57% of teenagers between 12 and 17 years old are regularly dating, and a third of them have a steady partner.
• Steady romantic relationships in high school typically last 6 months for 16-year-olds and about a year for 17 and 18-year-olds.
• Most high school relationships last between 5 months to 2 years depending on the age group.
• Only about 2% of high school relationships last.
• Less than 2% of people marry their first love.
• Only 25% of high school sweethearts last after graduation and make it to marriage.
• The high school sweetheart divorce rate is 54%, which is 21% higher than the average American rate of divorce.

In summary, the percentage of high school relationships that last is relatively low, with most relationships lasting between 5 months to 2 years and only about 2% of high school relationships resulting in marriage. The high school sweetheart divorce rate is also higher than the average American rate of divorce.