OP being a 'nice guy' just isnt enough in this world. So there are 2 paths you can take to what your idea of 'success' is. The first path is the short path down a well made road that'll lead you to a comfortable little pub with nice barstools and some quality beer. But after you've had your few pints, you realise you've got no money left, and nowhere to go and nowhere to stay. The first path is changing into a sh***y guy. Then there's the second path. The second path is a hike up a mountain, in terrible weather, but this path will lead you to heaven itself. This is the path of a great man.
Change yourself into a great man OP. Work out and get fit, lose all the fat. Fix up your diet while you're at it. Go out, go to clubs, go to pubs, meet up with some friends. Doesn't matter how superficial they are, you'll run into someone like yourself soon enough. And eventually you'll get a group of great people. Eventually you'll run into that great girl, and have a great life.
Just think about what happens to those bad guys. It's not a happy end for them. Their partner leaves them, or they get stuck in an unhappy marriage where they end up as deadbeat dads whose children detest them.
I know it can be depressing at times, there will be days when you just think 'Im a failure, there's no point in going on anymore'. Push through those days. Just keep pushing through, and at some point you will realise that you've become a great man.