I don't think we are going to make it to the wedding---please help---men and women!?

Ok we are supposed to be getting married next year on Valentines Day. My fiance was over and he left his facebook page open by mistake. I found several messages of him arguing with a female I know nothing about. The messages pertained to him picking her up for school and she invited a friend of hers to come along. He never told me he was taking her to and from school and all of this is new to me. Then I found out that he took his son over to her house to play with her kids. There are kids that live downstairs from them so why did he have to go over to her house.Then he told a clmate of his to bring her y azz to cl. He explained and said that she was on fb--with a stat saying she was feeling y--and that is why he said that. Then some other girl texted his phone asking him what he was doing. I took the phone and asked her who she was. She never responded but turned around and called him and asked him to ask me not to text her anymore. I wasn't rude or anything I just wanted to know. He claims that he doesn't have any privacy---but I work a full time job, a part time job and go to school full time. I'm never at home so he gets to do whatever he wanna do so why do he feel like he has no privacy. I don't like going through phones and emails but I don't wanna find out after the wedding that I am married to a cheating POS-----any advice on what I should do?