Why am I so bad at endgames?

I just lost a chess endgame with a godforsaken material advantage of +13, I ALWAYS seem to lose every single endgame I'm clearly winning, why?

Just picking out one key moment from this game (there were other mistakes as well which contributed to your loss)...

You had done all the hard work and achieved a huge material advantage when you reached this position.

Here you played Qxe4+. Whether or not this is technically the best move is not really important - your material advantage is so great that the only way you can lose is the way it happened - that your king gets caught by a counterattack and that some of your pieces are still not in the game. So here an automatic move should be to exchange the queen's and pretty much remove the possibility that your king will ever be in any danger. Then you can win easily with your extra material. It wasn't necessary to capture the pawn on e4, even if it was with check and even if there might be some forced checkmate for you there - if you don't see a forced mate just simplify and make it easy for yourself. You already have easily enough extra material to win, so one more pawn makes no difference. 

Thank you for your advice

Or to put it in another way: you lost because you did not play an endgame in spite of the title of your post. As long as queens are in the board we do not speak of an endgame unless they are the only units beyond pawns. This is a middlegame with your king in danger and you should do as Strangemover advises.

Yes, if you have such a material advantage you always have to exchange as much as possible. Here first the Queens and then you should have a look to activate you pieces. After the queens are gone you can try to activate your king because now you are in the endgame and your king is a fighting piece now. After: Qxb3 Kxb3 Nd7 Rd1 Nf6 e5 Ng4 Bg2 Rb8 you can bring your rook on h8 into the game and start an attack. You can bring your King to c7 for example to get out of the pin.

I have "Silman's complete book of Chess Strategy" from 1998 the price was only $10.00 and it is in pristine condition. It starts out with many openings and that’s where I picked up “the Grob.” 

When I pulled it on many players, they hated it because they didn't like my first move. G4 They didn't know how to respond. Silman says that the grob is an opening that should not be used because it losses the f4 and h4 squares.

I like that book because it covers about 50 opening in alphabetical order and then moves onto the middle game, which would anyone. The "end" portion is covered as well.

The book is very easy to understand and all examples are short and to the point. I read 175 pages of it then hopped to page 300, as I wanted to cover the endings with few pieces and pawns. I love this book. That one I recommend.

I have another “Silman’s Complete Endgame Course” From beginner to Master 2007. It starts with entries for "unrated to 999." From there it goes to "1000 / 1199" and continuous up in "200" increments until it reaches "2400." I also recommend this one. It will always be good till you get to be a master.

So if you are rated, you can begin at your rating or look back and check what you already should know and learn it if you want to. Then you can improve from your rating.

There is another series by Russian grandmaster "Lev Alburt" it is a series with grandmaster "Nikolay Krog­­­­ius, "Who the heck is that?" He is the man Spassky insisted as his special coach, he has trained many Russian grand masters. I recommend this set.

"Chess Tactics for the Tournament Player" 2005

"The King in Jeopardy" 2005

"Chess Strategy" 2005

"Just the Facts" 2005

I recommend Lev's series.