I've been in a relationship for 4 years. Last July while on vacation I pulled a towel out of the towel rack in our motel room and a phone fell to the floor. I didn't think anything of it. I came out of the bathroom and said "look, someone left their phone in the bathroom, I'm going to take it to the front desk and turn it in." My boyfriend instantly freaked out, grabbed the phone and ran out the door. I was standing there in shock wondering why he would react that way. I turns out it was his secret phone that he had used to sign up at a dating website and was texting women with. We had a huge fight and he was remorseful so I figured we'd try to work it out.

Flash forward to New Years Day, 2015. I went to his house early in the morning and there was another secret phone laying on his counter. I picked it up and started reading the text messages. I couldn't believe my eyes. He was texting these women as if they were in a relationship. I went into his room and started screaming at him with the phone in my hand. He grabbed it and wouldn't give it bad. I stormed out the door, so upset. After about 15 minutes I went back inside and asked him why was he doing those to me. I got the standard answers from him. "I wasn't feeling fulfilled, it's just cyber BS and it doesn't mean anything, I have an addiction". He had left the phone on the counter again so I grabbed it and ran out the door. Then I waited for the women to start texting him, and they did. I answered each text and told them what was up. He had the phone shut off and I called and had it turned back on, which really made him mad. He told me it was none of my business. Pardon me but I think it's totally my business. He claims that he never had any intention of actually meeting any of them but I'm very skeptical about that.

I just don't understand why he keeps doing this. Does anyone have any insight into this behavior?