Almost cheated on my girlfriend by fucking my sister

I am m/18 she is f/20 there was a house party my girlfriend was in it too after a few drinks me and my sister went out to buy a few things thats when it kind of happend she grabbed my hand and placed it on her ass while walking in kind of a isolated zone i asked what is going on she placed my other hand on her chest and said take the hint dude so i asked you wanna do it she kind of blushed placed her hand on my dick and rubbed it a little so i asked her about not revealing anything to anyone she said almost the same thing i told her because i have a girlfriend it'll be hard that night after my girl went home we were sitting next to each other watching anime when it kind of started she slid her hand in my pant i started rubbing her nipple squizeing her boob then i slid one hand in her pants started rubbing her clit gently slowly picking up the pace btw this is all occuring while my mother and younger siblings are just a meter away my mom was sleeping tho after this experience i asked her lets do it we went down to the only room that was empty making up an excuse of being hungry went down we both unzipped our pants took them i started by sucking her nipples slowly then my dick started growing i did'nt have to say anything she went down on her knees and started licking the tip of my dick slowly taking more and more in her mouth i even asked her have you done this before she replied nah bro i am still a virgin never did anything she sucked for a while longer then i went down on her started licking her clit until she came unfortunately some started banging the door so we had to get back to acting i kind of feel a little guilty for my girlfriend but i know this sister brother thing has no future we both agreed on fucking for fun but we have'nt fucked her even once you guys may think i am dumb or something but i was maybe just guilty so now i leave it up to you guys tell me what should i do and maybe how should i take her virginity.