I Start to Embrace My Step-Son's Sex for Chores Agreement

So.. as the months progress, and my step-SON has held up his end of the bargain everything has been going extremely great. One night as we finish up dinner and he so kindly offers to take my empty dish and do the dishes (without being asked) he then awkwardly approaches me with a question. He is still a bit nervous about my reaction when he asked to cum in my face a few months ago and so I have to coax the question out of him. It turns out he wants to push things a little further, to blowjobs. At first I am WAY against it, however, I make him a deal that requires even more responsibility. He has to not only get a job, keep up with all of the chores, but keep it for at least 3 months. After that, he can have his blowjob. It turns out, he is committed, he keeps the job, gets his blowjob and we agree that as long as he keeps it that he can have one a month. After months of this, while I am giving him his blowjob I finally ask him why he hasn't tried to press me to have sex yet. At first apprehensive, it puts me in the position of begging. Which, in the end I do, we re-negotiate another deal that allows him to have full control of how often, what positions, and where he gets to cum. I want it so bad at this point I stop mid-blowjob and I let him fuck me for the first time. He of course, chooses to cum all over my face.