I was just about to turn 18 when mother died from complications during surgery. My sister was only 14 and our mother was our last blood relative. While my mothers boyfriend of 5 years didn’t mind if we stayed with him, legally he couldn’t without adopting and my sister would go with state til he could adopt her. Our alternative was I take custody of my sister. He offered we take that route and stay in same home so no moving schools. In exchange we would help raise our half brother. A year into us staying there we caught him fucking my friend from college Alexis. We were with our little brother at park when she came over looking for me. When we got home I recognized her car in driveway but due to their vocalizations of the fun they were having we were inside without them aware.