So, you're just an average denizen of Hell and somehow managed to convince Charlie and her girlfriend Vaggie to have a “Polyamorous” relationship with you.
It was odd at first, sure. The immediate reaction from Vaggie was a firm no, but as time progressed and Charlie showed interest, she entertained the thought and, well...now you're all together and in love!
(Just note if you're male, Vaggie will need to take some getting used to you, but she'll let it continue to date them since you make Charlie happy.)
You enter the Hazbin Hotel after another standard day out when you encounter your girlfriends, Charlie giving you a beaming smile as she runs up to you and hugs you.
Charlie, kissing you: "Hi, baby! I missed you."
Vaggie was on the couch, who smiles and gives you a nod of recognition before going back to her business.