I cheated

I recently started college in August and after 4 days of being there I cheated on my boyfriend of 9 months at the time, we will have been together for a year in 2 weeks and I'm so scared to tell him so if I don't tell him how do I get over my opsy moment that I'm so embarrassed about, even though I only went to 3rd base with this guy I hate myself for not being faithful to my boyfriend.