Who was at fault for us breaking up?

Ok so this will probably be a lengthy wall of text explaining backstory etc but please bear with me. My girlfriend of 3.5 years and I broke up about 3 weeks ago and I am not really sure whose fault it was or just any advice/comments from anyone especially anyone whose found 'class' to be an issue in relationships. The backstory: We met at the start of 2nd year in Durham ( October 2009). I come from a very middle class background: private education, only child and from Surrey however she came from a single parent council house (although very intelligent, well spoken etc) near Maidstone (Kent). The start was very rocky - frequent class issues caused us to almost break up several times very early on. However I will add it was never from side, I don't ever judge anyone and view everyone equally however she seemed to have real issues that I came from a better background than her. We broke up for about 6 months in January after she slept with her ex twice which as someone from a family where her dad walked out on her mum I just couldn't fathom??! I had never been cheated on ever before and was totally not prepared for it especially how attached to her I had become in such a short space of time. I did not take it well and ultimately was the catalyst for a depressive spiral that led me to drop out of my second year at university. However I met a new girlfriend, probably a rebound however nice all the same, and as soon as it went on facebook the ex was on the phone "how can you be over me so soon" "i still love you" "please give it another chance" etc. I knew I was still in love with her and decided to give it another shot. This time I was more cautious about getting overly attached however always had this sense of paranoia in the back of my mind. My ex has M.E. and it comes and goes through bad phases. Third year (or second year again for me) was a very bad patch for her and I ended up virtually becoming a full time carer for much of the year which I have no illusion detracted from my work (not to mention dropping out the previous year led me to forget a lot of my maths). However I loved her and felt it was my duty to look after her even if it meant being at her side all day on the really bad days and never felt angry at her for it. I helped her with her essays and revision, again at the expense of my own, and she graduated with a 2:1 in Anthropology and Archaeology. Come fourth year (or third for me) and she is now back home and I am still in Durham. She didn't handle the long distance well and insisted on phoning every night and then complained if I was saying I was going "only 20mins" into the call. I always said I'd rather a long phonecall every few days when I have things to talk about rather than every day when I don't necessarily have anything to say. The relationship became depressive, I missed her when she was gone but when we did see each other it was difficult and stressful. I fell out with my college rowing club which till then had been my only sport/social activity and led to another depressive spiral and this time medication. I rapidly put on weight, due to medication and stopping rowing, which my ex was always pointing out and complaining about (only further compounding my issues). I was offered to resit the year again, in hindsight something I should have done, however I just wanted to be done, get out and be back with the girlfriend. Results didn't go well, as expected, and I graduated with a 3rd (June 2012). Now wind forward to the start of this summer. Its been a year since I graduated, two in her case and neither of us have a job. I decided upon accountancy however with a 3rd I knew I was facing an uphill struggle and so studied the first 6 ACA exams independently in the hope this would mitigate my degree and prove to firms my true potential (bearing in mind 4As at A-Level too). However it didn't work - medium/big firms didn't even offer interviews just citing my degree qualification and then small firms didn't want me for a lack of experience so I was caught between a rock and a hard place. I applied to well over 100 firms all the while my girlfriend, and her mum (who wanted her out of the house), were saying "oh you still haven't got a job yet" and generally making life even more stressful. Ultimately after talking to someone about what I could do to get into accountancy I decided upon re-applying to do a 2nd undergraduate degree (into accountancy). At this point my girlfriend, and her mum, were just saying "just get any **** job and some money forget accountancy". Easy for her to say, she'd applied to a grand total of 2 jobs in 2 years since graduating (and bear in mind she was much better now) and had effectively said she wanted to live off me. I had always compromised so much for her and I decided to make this decision for myself as I'd never been so motivated to do anything in my life. I tried to reason with the gf, explaining how much it meant to me and how 4 years is a drop in the ocean when you think we'll be working to 70+. I also said "just earning a salary isn't enough to compensate for lack of job satisfaction and potential etc". She still was so against me going to university for long distance reasons so I chose only local universities and even said we could mature accomodation together etc. I thought I had convinced her then a couple of days later she informed me she'd met a guy in a club and had organised a date with him. Almost seemed like a retaliation at me applying to university? And that was that. I really don't know what to think about the whole situation and how to make sure it never happens again?

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