I didn’t know if you wanted me to put the variations on a board or if you were just fine with some crucial moves being written out, so I just wrote them. Obviously, at the SDK levels, a lot of minor things that could have changed, but I will highlight your biggest mistakes, and some of your opponents mistakes as well, especially ones you did not take advantage of. I didn’t do too much in-depth reading, so obviously I might be a bit too hasty in my analysis, but I think it will help.
If you have a few specific questions about why your variations were not optimal or
Move 23: S7, should have played F5
Move 33: Big mistake.It is an even game till this point, because on Move 32 he plays S16 instead of Q6, so here you must play C12.
Move 39: N7 is superior to O8.
Move 47: K8 over L7.
Move 71: Ok, this is pretty big. You were losing early on, and he made some blunders to make the game basically even. He fumbles big on move 70 by playing P2 over K9. You should respond O13 but you play T3. You assumed he had sente, but it was a gote move.
Move 81: B12 over E10. F6 by him was a mistake, and you once again responded instead of tenuki. He is then throwing his whole lead by playing E12 over K2. There you play E2 instead of P13, which would have been much better.
Move 159 is where I would say you definitively lost the game. You would fall behind, he would blunder, you would make a sub-optimal, but not usually optimal move to bring it close again, and the war was waging. I don’t really want to do much more because it would be too long, but also, you should not feel bad. For all the mistakes I have pointed out, you played many good moves too. I would say the biggest thing you should look at is do not instinctively respond, but look at possibility of tenuki and his moves being gote.
Hope that helped.