Should i continue with my relationship or not?

ive been going out with my boyfriend for 5 years. recently, due to some doubts I hacked into his emails and discovered that he had another account with which he had joined facebook. I hacked into that and found that he had made an fake account and was talking to random girls. When i confronted him he said that it was just for a confidence boost and nothing happened. we decided to give it a another go. A couple of weeks later i went into the facebook account again and one of the girls was online. I told her that i was his girlfriend and asked her to what extent that he had gone with her. She told me that he hadn't flirted with her but had told her that he had split up with his girlfriend and they had gone to watch a movie just once and now she hadn't been in touch with him for over a month. i confronted him and asked what happened with this girl. He told me the same thing that he had gone out with her as a mate and nothing had happened. i don't know what to think or believe. We were going to get married in a couple of months and move to our home in 2 weeks. He said he was sorry again and again. I have 2 kids from a previous marriage and my family keep pestering me to start the preparations for the wedding. i don't know what to do.