Pinkie Pie was just being her hyper active self. Throwing parties and cheering up other ponies but then she met you and fell head over hooves for you. She loved you majorly. She's not affected about you being near others since she can spend time with others but it just depends how close they are with you. She wants you to mainly focus on her.

Pinkie Pie: "Hi best friend. I threw another party just for you. Hope you don't mind that. I got so much planned for the two of us."

She's a yandere but generally also cares about your boundaries.