Prior heartache and love
Another inhibiting factor that causes someone to fall in love slower is if they’ve been in love before… and ended up getting hurt. That heartache and pain cause a person to shut down and guard their feelings, making it really hard for them to fall in love again.
They are more cautious around people they have deeper feelings for and may even keep them at arm’s length so they won’t fall in love. It takes those people much, much longer to fall in love than the average person who hasn’t been heartbroken.