Speaking as a mid/high plat support mage main, here are my takeaways:
1.) Them having Singed and Kogmaw suggests to me that they will win a late game slog, and thats exactly where the game went. Morgana is solid late game, but nothing amazing. The other two champions can straight up carry the game. You guys needed to group up more, and seek to end the game earlier.
2.) The death count between the teams suggests that you had the better players all around, but they outscaled you. The game went on so long because your skill kept you in the game for a longer window, but with them continuing to outscale, it turned into a 50 minute slugfest that they won.
3.) This is a smaller factor, but still worth mentioning - they had a better frontline, and more ways to protect their champions. They also had some great counters to Zed and Kat. Ziggs and Teemo can really do area denial super well, and once a teamfight starts and they bamf to the backline.. that leaves... you to protect the adc alone? they had a teamfight advantage, it wasn't huge, but they definitely had one.
4.) When games go this long, teamfights are generally ALL that matters, that and who gets caught out. Grouping up at the late stages of the game is a critical skill to learn, and one not a lot of players understand.
5.) Your loss had absolutely nothing to do with your build items. Trust me. You were fine. You can't really blame yourself - instead focus on your own play. Look at your death count. Try to die less than 5 times per game.
6.) Last point, Checking your match history, I Feel your a good player from your KDA and you seem to pick good champions, but your lane and champion picks look a bit all over the board - Pick a favorite and play them more often, play into your BAD matchups so you can learn how to handle that. Mastery will help. Don't put too much stock into 'who counters who' .. instead look at late game carry potential, and who you are your absolute best with.
Hope it helps - cheers :D
