Does she know that you created this thread?
It's true that you're talking about her behind her back?
“You are fooling me, you are lying to me, you are cheating on me”
Tell her "I do talk to other girls when you're not with me. It is possible that I might one day end up sleeping with one of them. If that happens, I'll let you know straight away. You have my permission to talk to other guys when I'm not with you. If you find one that you think you'd prefer to me, you have my full permission to have sex with him and start a romantic relationship with him... If you want to dump me now, or at any time, for any reason, or no reason at all, then you should go ahead and do so."
“You and your friends are laughing at me behind my back as you cheat, everyone is laughing at me and you are fooling me”
Tell her "It's true that we do talk about you from time to time. And our conversations aren't always serious. I'm sure you exchange gossip with your besties too. That's fine. You can chat **** about me all you want."
“I’m disappointed in myself again for trusting you”
Tell her "I'm not asking you to trust me. You should never totally trust any man. Ever. It's up to you if you want to carry on spending time with me. If I haven't done enough to motivate you to want to spend time with me, then the fault is mine. And you should dump me."
This happens whenever I’m doing something on my phone e.g. if I go to the toilet with my phone
Don't take your phone to the toilet. Take the newspaper or a copy of Viz.
Has she been consuming a lot of inflammatory food or drink? The type of stuff that causes internal inflammation?
High salt foods? Alcohol?
Or the sort of foods that gives her a blood sugar rush followed by an insulin flood?
Try feeding her high fibre meals, washed down with water.
And giving her lots of fresh fruit, especially berries to snack on.
How often do you go on fun / interesting / adventurous dates with her?
Is it at least once every fortnight?