To get this you have to get through 9 levels for Cassie. Each level has up to 4 goals you must complete to reach the next level. The possible goals are, reaching a specific number of hearts, reaching a specific amount of money, giving specific gifts, taking the girls on dates, reaching a specific level in your hobbies/jobs.
The goals for Cassie are
Level 1 Adversary
100 Hearts
100 Dollars
Level 2 Nuisance
250 Hearts
200 Dollars
Level 2 Suave
Level 3 Frenemy
688 Hearts
Level 3 TechSavvy
Level 3 Buff
Shell
Level 4 Acquaintance
1891 Hearts
750 Dollars
Work at Restaurant
Rose
Level 5 Friendzoned
5672 Hearts
Hand lotion
Level 5 Motivation
Moonlight Stroll
Level 6 Awkward Besties
17,016 Hearts
Donut
3 Moonlight Strolls
Work at Lifeguard
Level 7 Crush
51,047 Hearts
Level 7 Badass
Fruit Basket
Beach
Level 8 Sweetheart
102,094 Hearts
Chocolates
3 Beach
Beach Patrol (Lifeguard)
Level 9 Girlfriend
204,188 Hearts
Level 10 Buff
Book
Sexy Lifeguard (Lifeguard)