Inherited Neighbor

I (32) live in an apartment building, and I got really friendly with one neighbor. He (34) was like me, a quiet person who never dated like me. Both were called nerds at college, and focused on our careers after college. Then his mother died of cancer, which shattered him, and his younger sister (29) came to live with him. She had been caring for their mother for years, their father had left years earlier, and they hadn't heard anything from him since. She was quiet-natured, like her brother, but even more so. It took her several months just to relax around me. Then her brother had one of his episodes, as he called them. A fainting spell caused by high blood pressure, caused by being overweight. He was heavily overweight, and I'm skinny, normally he would recover. But this time, he was at the top of a flight of stairs and fell down the stairs and died because of the fall. He always knew that one day his fainting would cause his death; everything he had, of course, went to his sister. A letter addressed to me was attached to his will, in which he asked me to watch over his sister if he were to die. I agreed to watch over her, and I was the only person she knew in the city. So, she moved into my apartment with me, and we carried on as before. Several months later, I was promoted, and it came with a transfer. So we moved to a new city, still acting as we had before her brother's death. My new job came with a socializing requirement, such as dinners and business functions. I could have attended on my own, but I decided to have someone accompany me; of course, I chose her. She joined me, keeping very close to me as if we were joined at the hip. Last Christmas, we attended a party and overindulged somewhat, not planned. The fruit punch was spiked or was alcoholic from the start. Either way, we got back to our apartment in a very playful mood. I can't remember how it started, but we became lovers. The next day, as we sobered up, I was very happy with what had happened. So, I made another advance towards her, and she just went along, and we fucked again. Needless to say, the cat was out of the bag, as they say. Without me asking her, she moved into my room and bed there after. We married in March, not just because she was pregnant, but we were living together as man and wife already.