Midlife Crisis

I 23 bought my parent's home when my father was transferred, I'd a good job and was staying put. I already knew all the neighbors and it was easier than finding a new place. An old friend 55 of the family, I'd known all my life lived across the street. She was now widowed and living alone. She worked for the city and tended her garden and never dated as far as I knew. A few weeks after my parents left, she came over to talk feeling lonely I thought as her and my mother had been always talking. The usual question did I've anyone special and how was everything going, and I was invited to dinner on Friday night as I had nothing on, I accepted. That became a regular thing for us to have dinner together once a week. Over a few weeks I noticed she was distracted and not wanting to get personal, didn't ask her what was wrong. A week or so later she straight out asked me to do her a huge favor, without asking what it was I said I would help her if I could. The favor was to fuck her, you could've knocked me over with a feather. Neither of us are anything special in looks or body shape either. But I did get aroused by the idea of sex and as she had asked me, I agreed. I stayed that night with her and thought that would be it sex wise. But she wanted more and as I'd already fucked her three times that first night and the morning after. I agreed to keep fucking her as along as she wanted me to. Now a year later we're still fucking once a week sometimes more, I've no girlfriend yet and no real incentive to find one. I believe she started having a midlife crisis and so we became lovers. But it makes her happy and I really enjoy the sex.