My mom and dad divorced when I was just 2 years old. Shortly after that my dad remarried and I grew up knowing my step-mom more as my real mom than my actual mom who I rarely saw (my dad won a majority of the custody).
I became really close to my step-mom and not as much to my dad who was an airline pilot and would be gone for long periods of time. When I turned 15 I had matured through puberty and my step-mom began to take notice. Little by little, she and I flirted more and more and eventually it led to us making out, taking off our clothes, and fucking. I lost my virginity to her. She was almost 20 years older than me. We regularly had sex whenever my dad was away for the next several years.
We kept our affair a secret until after I graduated college. School put a bit of a strain on our relationship at first as we saw each other less the first year of my college. She started visiting me more often and was getting tired of my dad. One year before I graduated they divorced. A year later I proposed to her and we are now married. My dad found out when we got engaged and we haven't really talked since. I don't really care. I had an amazing step-mom who is now my beautiful wife.