Besties

Sometimes people just “click,” best friends forever. It happens to digits, too! In some columns, and some rows, certain pairs of digits are inseparable.

Rules:
Normal Sudoku rules apply.
Digits within cages sum to the small number in the top left corner of that cage.
Digits outside the grid are adjacent in some order in that row or column.

Estimated difficulty: 1.5 out of 5