Useless at love newbie!

Hi guys, I'm new on here, I'm Azz. Just thought I'd say hi and seek some help for my repeated failings of my love life. I'll try not to bore you all too much with the details but it is as follows:-

I was a really happy horny and confident lad in my early 20's, had a few relationships along with some flings and then at 22 I met who I thought was the girl of my dreams and fell madly in love. Things happened when we were together, work problems and money problems etc and I started to change in myself, found myself getting withdrawn, distant and lose interest, was watching porn rather than having sex with my girlfriend, including her catching me in the act at times. I lost all my confidence and my ability to be sexually active with her, often going for weeks without making love. Also, I just wasn't interested in her emotionally and gave her no love. I was diagnosed with chronic depression. In the end, and quite rightly so, she left me. We had a mortgage together, were engaged and were talking about kids. It's wasn't until after we split I realised how much she meant to me and how much I loved her. Two years on and I find myself living with someone else who I care about so much, but I'm back in the exact same situation again. Would rather masturbate rather than make love, not really very affectionate etc and just generally not happy. I still think about my ex every day, miss her like crazy and it hurts. And I constantly think what if I'd done things differently. I look at other couples out and about and just wish I could be how they were. I hate myself for how I am.

Suppose what im asking is what's wrong with me!!

Help!!
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I suppose what