People that have a good amount of common interests establish a basis for falling in love in the future.
As they get to know each other and share time, they develop a stronger bond.
This bond leads to more personal information being divulged to each other.
This is multi-layered personal information, including that which neither party is all that proud of, but is open to sharing due to the level of trust that has developed.
You left it to him to keep the relationship fun and exciting.
Now that he is comfortable in his relationship with you, he isn’t putting out anywhere near the same amount of effort to show you a good time as he did in the early months of the relationship.