What should I do about my sleepwalking?

Need some help!

I’m 18 and I have a boyfriend and girlfriend. They both know about each other. They are o.k. with it. That isn’t what I need help with though. I need help with something else. I have an apartment that I share with this cool, incredible 19 year old. We each have our own rooms. When my girlfriend spends the night I sleep fine and nothing happens throughout the night. The problem is when my boyfriend spends the night. I love him and he is wonderful. We have great sex but that stuff isn’t the problem. At night while we sleep, he has told me that I will sometimes initiate sex. I believe him because he has even shown me the fingernail marks on his chest. That is a big problem because I don’t remember any of this. He says I’m like a different person when it happens. That is difficult of course but there is something that happens even more frequently. I will get out of bed and get in bed with my roommate. I don’t remember doing this but I wake up in the morning in her room. She said it didn’t bother her at first but then it happened while her boyfriend was with her. In the morning, I was so embarrassed. After that she started locking her door at night. This only happens when I sleep alone. Now that shes locked her door, I’ve begun waking up in strange places. One time, I woke up outside the apartment. That was the last straw. Now I need help. My life is turmoil. I started seeing a therapist but I still seem to be having problems. Does anyone know if there’s a way to stop it?