The Grim Adventures of Billy and Mandy (2001)

S3E1 Spider's Little Daddy

During a father-son picnic, Billy stumbles upon his arachnid "son," Jeff, in a grimy restroom. Jeff attempts once more to win Billy’s affection like a devoted child, but Billy is still horrified by insects. Observing the situation, Mandy advises Jeff to adopt a tougher approach to capture Billy's interest. Following her guidance, Jeff finally loses his patience and traps Billy in his web, compelling him to confess his love for him.