Welcome to the forum. I kw it must have been hard to talk about waht you think of as a series of failures, however on thinking about your story I have come to the conclusion that firstly things can improve out of sight and secondly I do not consider you an unfaithful person, quite the opposite.
That attitude may come as a surprise to you so let's talk about that first. You had a best freind from school, a real person you you could be with , see, listen to and maybe even hold. Then things changed. Often school friendships stop right there as people go in different ways, You and your friend continued, but in a completely different way, as a long distance relationship, I'm guessing mainly via Skype or similar.
This is simply not the same -nothing like. Also it is not immediate apparent how different it is. If you think on it you may realise what some of the major differences are. It is basically an unsatisfactory thing after being physically together.
You stuck this out for 2 years, then felt the attractions of a living breathing person. Misguided loyalty made you break off and tell your freind, who did not display much understanding or empathy. OK so later she came back, however it looks like a long distance relationship was all she was prepared to have, and ended up stringing you along, then leaving for another. Not much "loyalty" there, thought to be fair she had probably found out too that a long term relationship was no substitute for a real person.
I'd suppose this has been your only venture into romance and the loss and grief, together with misguided self-blame, have turned your life upside down. You have not been in the right place to make good decisions and are now suffering physical as well as mental effects.
May I suggest you go see a GP in an extended consultation and describe what has been happening, all about your guilt, shame, poor decisions and physical effects. See what happens. I'd not be surprised if you found the whole matter had started to affect your mental health.
The money? Well if it was me I"d go see a financial counselor in Anglicare and see what is best thing . The job? Maybe seeing a uni student councilor and find out your options. Perhaps there is room to continue part time
I'll leave talking about family for another day. As far as I can see all you are guilty of is inexperience, something we go though and learn from.
I hope you return and we talk some more