I'm scared to tell him

When I was younger, about 8 years old my two oldest brothers got into a huge, really horrible car accident. Unfortunately 11 years later this accident still follows our entire family, each in different ways. For me unfortunately it's with wetting the bed. Ever since that accident I started wetting the bed, one doctor finally asked if I had any traumatic experiences when I was younger and the accident came up, he recommended I go to therapy and he's more than 100% sure it'll help me. My only problem now is this, I've been with my boyfriend for 4 years, we're building our home (yes at 19, no our parents are not helping us) getting married beginning of 2016 and I have yet to tell him. No one other than my parents and three older brothers know about this and I'm so scared and embarrassed to tell him because obviously it's a huge deal if I'm going to be in bed with this person forever. It doesn't happen everyday, but it happens offten. I know after 4 years and getting married soon he should know but I've never had to tell anyone about this and now that I'm grown and have to tell someone about it its really scary and gives me anxiety. What can I do? :(