Insecurities..Its Kinda long Sorry

So In The Past 2 Years Ive Gained Around 60-70 Pounds...I Was Around 180-90 Pounds Now Im 240-250..so With That Being Said...Ive Been Insecure About My Arms For Majority Of My Life...But Now That Ive Gained So Much Weight Its Worse I Will Not Wear ANYTHINGGGG Sleeveless Unless I Have A cover Up That Goes To My Elbows Atleast All I Wear Is T-Shirts With The Sleeve To The Elbow...And My S/O Noticed And Asked Me Why ..And I Told Him and He Always Always Tells Me Not To worry About That He Loves Every Part Of Me And he Tells Me i Should Be More Confident And Stop worrying About What Others Think...But I Cant Help It Ive Seen Girls Way Bigger Than Me And Their Arms Arent Anywhere Near As Bad As Mine....I Really Want To start Losing Weight Moreso In My Arms Than anything....I Just wish I could Be More Confident Ans Its Starting To Get Really Hot So This Tshirt Thing Is Getting Bad Cause It Makes Me Sweat Alot...Do You Gals Have Any advice Or Encouraging Words For Me ? Btw Im 19 No Kids Please Help Im Desperate