I was once-unknowingly. Someone I worked with and went to college with and I became friends and went out a few times. I thought it could lead to more than friends, but found out he was engaged! She was a very sweet, quiet girl and I was (at the time) a lively, hairdresser and I think he was just curious about someone who was VERY different from his future wife. I put an immediate end, but thought in my heart, if we kept going out he might leave his fiance. But I just couldn't do it. Funny thing is, he married her, they had 3 children and all came to my school and I saw him regularly and we actually bacame friends again. And I was delighted I didn't continue the relationship and marry him!
