Why am i doing this

We was drunk and had some friends over for a joke at first someone said to my girlfriend I’ll give you £10 if you show boobs she said ok without asking me but we was havin fun then she got asked to suck me so she did and later a friend of my friend asked are you willing to have sex and I’ll give you £40 so we talked and agreed no one else knew after he did it he said he’s got mates who would pay for this so tuck is number few days later again at home was havin a drink we decided to ring him 3 of them came round and had sex with her paid £40 each then when we been sober my girlfriend ask about doin it more and make money so done it 5 more times now and I’m regretting that we started this people coming havin sex with her it only started with bit of fun