From experience I'm going to give you a probably correct guess based off what I saw. I've completely ignored your actual skills
3 problems
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looking at your runes I bet you're not actually set up for a game that matches your slow game building.
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you lose almost every game that goes past 30 minutes.. Something you're doing is falling off lategame and its not just your runes.. which are probably also falling off lategame
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tear jayce isn't something you are going to carry yourself with if your team sucks. Especially with your burst masteries. How long does it take for you to get muramana anyways. I doubt its anything reasonable since your loss streak ended after you ranked up after a few wins with that one time trick.
I suggest having another look at your runes and thinking more deeply about your champ, build, and what parts of the game (timewise) you actually excel in as opposed to what you're trying to excel in.