All Stan ever wanted was to go sailing with his brother

but Stanford chose mysteries over him until it was too late…

Stan probably felt the same sadness when Dipper and Mabel chose to chase the gobblewonker than spend time with him. He was being replaced by mysteries again.

but in the end Dipper and Mabel realised what was important. Spending time with their Grunkle and although it may not have been with his brother, Stan had his dream come true, he got to spend time with his family, with the people he loved.

look how happy he looks.