The defence your opponent used is called "The Black Knight's Tango", the main line is usually 1.d4 Nf6, 2.c4 Nc6 - the game though, reminds me of how I played when I rushed into things, everyone at my club was telling me to slow my game down and think more so I did and I'm playing better than 6 months ago... tbh any game against a 125 is gonna be tough, maybe you just let it slip because you had an advantage from the opening and thought you had an easy win ahead - it's where I'm going wrong with white almost every game.