Bill is trying to show Dipper that he's a better demon than before. Dipper is 20 and Bill is like a million or more.
Mystery shack
"Leave me alone Bill!" Dipper angrily said slamming her bedroom door at Bill's face.
"I swear I've changed Pinetree!" Bill pleaded and rubbed his nose.
"Ha! Like you could change! Now leave me alone!" Dipper yelled behind the door.
"Okay." Bill mumbled sad he walked away to the living room where Ford, Stan and Mabel are there glaring at him.
"Bill you tried to start weirdmageddon!" Ford stated inching closer to Bill "I ought to send you back to once you came from!" He swore pointing a gun at Bill threateningly.
"Hey don't hog him!" Stan said pushing Ford aside showing off his brass knuckles "I wanna bruise him a little." He swings he arm but Mabel caught his arm "Mabel!?" He asked not understanding.
"Look guys Bill's done some messed up stuff but can't we hear his side?" Mabel suggested then glared harshly at Bill again "Than we kill the scumbag of a demon to nothingness." She suggested.
"Look guys I've spent some time learning about myself and the wonders of real! friendship and love so please I'm telling you my past is not today!" Bill begged.
"Really?" Dipper asked eyes red from crying. She came downstairs and looked at Bill's eyes they were crying as well and looked sincere?"I'll give you another chance." She stated and looked down "You broke my heart Bill." She added looking away.
"I know." Bill said making a floating heart that's in two before he rejoins the two making a beating again "But together we can love again." Dipper nodded taking his hand.
"Okay I'll give him a week before I start shooting dream demon heads off." Ford stated putting his gun away "So no more weidmageddon?" He asked looking for a yes.
"If that will make Pinetree happy then so be it." Bill said smiling not evilly but in a not so twisted way not like he ever has before.
"It will thank you Bill." Dipper said smiling at him and leaned for a sweet kiss.