Saying "You did alright for yourself" here means "You did well to find yourself such an attractive girlfriend". Anytime somebody "does alright for himself", that person has had success at something. People often use it when they compliment somebody for professional success.

Do something for yourself meaning?

: rather than have someone else (do or share something) She did not like just hearing of other's travels. She wanted to see Europe for herself.

What can you say for yourself?