Need help.. Relationship ending..

My name is Richard. I am 20 years old.
I have been dating the same girl for almost 2 years now and I am absolutely in love with her.
In the beginning of our relationship I had the chance to do a threesome with her and her friend, they are both bisexual and it sounded great! Well when the day arrived my girlfriend got screwed on her service hours at school and had to volunteer at an animal shelter that day, me and her friend were waiting for her to get done and come over when we had sex. Afterwords I felt horrible and I called her crying because I betrayed her trust..
She forgave me.. I have a very flirty personality and it got me into a lot of trouble, I flirted with a few girls online with no intention of hooking up, I just liked the attention, and she found out. She cried which in turn made me really upset.. After a week she forgave me again...
I think she let me off the hook too easy, cause I went and did it another 2 times. Which she broke up with me for about a month and a half.
We finally got back together December 31st 2013 and I have done everything to make sure I didn't **** this one up. I gave her all my passwords so she can check whenever she wants, I give her my phone so she can check whenever she wants, because I have nothing to hide. I learned a hard lesson about losing something as good as she is and I wasn't about to mess it up again.
Well now she gets mad at me over the smallest things, and we argue a lot, but I always appologize for being stupid and I have always said I love you after every argument cause its true, I really do love her.
Today april 4th 2013 she tells me she wants to break up because she can't handle the stress of being with me anymore.. I'm completely heartbroken.. Her best friend told me she had been telling her for a while that she was going to leave me..
How do I stop this from happening?
I can't sleep and we both work at the same place. How am I supposed to work with her without feeling alone and sad when she doesn't give me that cute smile I am so accustomed to seeing..
Please help, I can't see myself without her..

Well, she IS going to break up with you, and she is free to do so. It sounds like she is tired of monitoring you to make sure you aren't cheating on her. This in itself is very stressful because she always has to be on alert to listen for lies. You set up this situation by your behavior. Now that there are consequences, you don't like it. When you were cheating all those times, did you ever think, "this would really hurt the person I love?" Did you ever think, "WOW, I can't see myself without her, so I better be the man she thinks I am." What was it that had you continually testing her limits?
Well, now that you know she's, "OUT," I hope you honestly learn from this and don't repeat it in future relationships. Cheating is very wounding to the person who is cheated on. And you hurt her over and over! And now she is NOT forgiving you. Good luck. Ann

Well I continually tested her limits because she wouldn't stop talking to her ex. Even when I asked her to kindly not do so. She said there was no harm in doing it. Until she was telling him how much she missed him and still loved him. I'm not condoning what I did, but I don't want her to go cause I truly do love her. I have distanced myself from all female friends and stopped hanging out with the boys when they go out just so I can spend more time with her

I'm really sad for your situation. If she was continually talking to her ex, I guess she wasn't 100% into you! Then you asked her to sever contact and she wouldn't! It sounds like you got even by cheating? So in some ways, you cheated on each other: she cheated emotionally and you cheated physically. I really support you in assessing your relationship values! What is OK and what is NOT OK for you in a relationship? Discover this and perhaps you can eliminate all the drama caused by cheating and talking to exes! Good Luck! Ann

It's hard to compare to a marine :/
I tried to out-do him by training to be a navy seal.
But I wasn't allowed to join cause I had knee surgery due to a football injury.
Thank you so much for your advice tho, I won't give up on her

Are you saying that just because you aren't a Marine or a Navy Seal that you didn't have a chance with this girl? Or that you had to sign up to put your life at risk to win her over? Honestly, badboyfriend, I hope you learn that you are a good guy without all that - or at least after reading your responses, I believe you have goodguy potential! Let me know when you decide to take, "NO," for an answer. I think she's given you a, "NO." Take care, and I wish you well, Ann

It sounds like you have low self esteem...you feel the need to flirt with others because you like the attention...and you feel inadequate to her ex because he was a marine?

It sounds like neither of you were 100% happy...you cheated on her, she kept telling her ex she missed him. It sounds like a toxic relationship. Once you lose trust it's very hard to get it back.

If you two got back together, I think you both need to set boundries and work hard on your relationship. It's not good to be snooping on your significant other (even if you allowed her to). & stop flirting with other women!

The day you cheat is the beginning of the end. She should have ended it the first time you hurt her and you were very lucky to get all those chances but yet you continued to screw up a second, third, fourth time..

You had no empathy for her feelings, no respect for her and you hurt her over and over again. You took her for granted and took advantage of her forgiveness. Now you need to pay the price for that so you can man up and learn how to treat a woman the way she deserves to be treated.

I dont care that she was texting her ex blah blah blah. If you were unhappy with her behavior-you should have walked away. Cheating does not solve anything. it only makes everything ten times worse and by stooping to her level or getting revenge you are just causing more pain and destruction.

You crave attention off other women because you are insecure and it strokes your ego. You will never be in a healthy relationship until you boost your self esteem and you also need to set boundaries, expectations and standards. You didn't like her behavior and your answer was to cheat which is pathetic. Next time walk away