I can see it's not the first time they've had sex together. It's so convenient - you don't have to take anyone off, there's always a shower and a bed nearby. Of course, her brother's dick is great, so any sister would fall for one and suck it at the first opportunity. Well, it seems to me, he doesn't mind having fun with his sister with it either - his own soulmate won't betray him or make him marry him. It was so cute when her brother came inside her - it just cheered them up. )
You're in love with him or with his dick.