Talk about your priorities. Discuss the things that are important to you and let the person know that doing well in school is at the top of your list. Explain that at times you may need to focus on schoolwork instead of him.
Manage your schedule. Keep a weekly schedule and write in your schoolwork as well as any plans that you have with your sweetheart.
Study together. If the person is in school as well, plan study dates. After you finish, put away the books and spend some quality time together.
Join a sport or club together. If you are really pressed for time together, then make time by signing up for an activity that you can both do.
Spend more time focused on your relationship during school breaks by taking a trip or vacation together.