Should I even bother to work things out and trust my girlfriend?Am I blinding myself from truth?

Well this is a long story and confusing situation may even sound childish.It is sad to say but my girlfriend and I of 4 years have been having serious issues. Pretty much the entire 08 year. I am truly in love with her but as the new year is coming in I want to have a fresh start either with or without her. This all starts back in April of 08 when I was ASKED by her to send an email from her phone n ran into a picture of a guy who was always trying to get with her back in HS years taken on her phone sent to the guy. So i didn't like it since I didn't even know she hung out with that "friend". I didnt think much of it and didn't even mention it at all but thinking back by that time we were beginning to have arguments over simple things. About a week after that incident I was using her phone to make a call and as soon as I grab the phone a txt comes in some guy saying something along the lines of "hey my love how r u miss you"I BLEW UP! because while arguing n askin she told me it was that person n the number was saved as sum1 else so she was trying to hide something.She also told me they ran into each other a "couple" times but i believed her it was nothing I should worry about but why lie and try to cover it up? After a long night she said its just because she knew I wouldn't like it and apologized and I asked her to cut that off because that guy is obsessed with her and I didnt like that. She said she would,but since then I began having trust issues.Well fast forward to about September I had an accident n became needy and I admit annoying even depressed.Well at one point I called n she was with friends i could hear guys and i would ask questions and we would argue specially because I wanted her to be there with but then she just stopped answering when she was around friends.Then one time i needed her and she didnt answer and so when she finally did I was so upset said hey you are there for friends not for me then she said she needed space..I BLEW UP!! that deeply hurt me since I really needed her, and told her to have all the space she wanted and said we were over!Well I love this girl and after that I did something dumb but don't regret because we had broken up and I wanted answers how can we just suddenly end and why the problems.through my own ways obtained her phone records and found out some weird things and my gut feeling was correct she had been talking to that HS "friend" almost every night for long times since about jan of 08 even like right after talking to me would then spend an hr or 2 on the phone when she had told me she was going to sleep, and I had felt like that might've been happening i think is what pushed me away and then i wasnt as nice or as loving like i normally am and caused all the arguments in between.Also noticed that since september a new number even worse it was literally every night and day txt and call while i was going through my issues when i needed her! Well I confronted her about it and as expected she blew up because I had that information.I was angry she would b going behind my back for so long and lie about it all the time when i would ask if they still talked.She told me that new number was a new "friend" friend of a friend from college some guy that got her number from another person and just called her up one day to tell her he liked her she said she thought he was cute but wouldn't do anything because she had me that it was just as friends.well at that point I said he was interested in more than friends and that there was no real foundation of friendship they didn't know each other why would she even let that go on?Well after all that she did apologize for all the lying and bs but said I needed to trust her.after broken up for few weeks we got back together and it was great but then I started gettin the feeling she was lying again and spending long time with this new guy on the phone again.Well about a week ago we were together and her phone received a txt as she looked at it I glanced over and the txt said was from the new guy and read "Hey baby blah..blah..." I withheld my anger and made believe i didn't see it and asked oh who was it she said it was her girlfriend asking a question after that moment on I was hurt felt betrayed and been questioning everything from our talks of marriage to her love. To make things worst last week we were together and my phone had died and I wanted to search for something and I asked her to let me use her phone she was reluctant to do so and kept brushing me off or changing the conversation till I noticed and said hey are you gonna let me use it?is there something you are worried about?she said no so logically i asked to see it again and she just didnt want to and started arguing as if I wanted to see her phone to look through it, and even if that were true why should she be so worried if there is nothing to hide?after that night she didnt let me use the phone (shes never been that way)i was PISSED and said I could one imagine wha