Why am I so irresponsible with my money?

I am now a 32 year old man. Same bank balance today as age 16: £0. Every month waiting for payday. Have never had a holiday with friends and I have not owned a car since 2010. I can never afford fancy clothes and I don t eat in fancy restaurants. I rent a cheap flat - probably the cheapest flat in London. I have about £4-5k of debt plus student loan debt £25k. I remember blowing nearly £5 of that on a car in 2004.
I use a pay as you go phone. I live alone. I am currently doing a Masters while working and for which I pay installments for fees. I have had long periods of unemployment between 2011 and 2014.
It depresses me that I have never had anywhere near even £1000 of money to keep since entering the world of work in 2009.
I currently earn about 1600 a month after tax. I am very ambitious and want to be successful. I have lived in my rented flat for 6 years but the place still looks awful and all I have ever done is purchase carpeting and cheap furniture over 6 years. I am too embarrassed to invite friends over and have never even had a girlfriend to come and visit me at home because of my insecurities. Sure I am not a bad person, I am not bad looking and I dress well even with cheap clothing. But I worry about even asking anyone on a date because I have to worry about my pocket.
How do people manage holidays and mortgages and kids and cars even with low salaries?
Every month feels like there is always things I need repaired or debts to pay off.
How do I change?

Read more: Why am I so irresponsible with my money?