Emotional Affair Next Steps

I met Scott a year ago at a work related event. We work in the same field; different companies. We are both married. We hit it off and have gone out for dinner/drinks at least once monthly ever since. We have many common work interests, but more recently, we've shared more personal stories as well. He always seems eager to get together and the frequency of getting together is increasing. He remembers almost every detail of anything I ever tell him. He even brought me back a souvenir from a conference I had wanted to attend but couldn't.

I know I am developing feelings for him and would like to take it to the next level. I don't know if he has romantic feelings for me, or just enjoys me as a friend. How can I tell if he is attracted to me? I want to be honest with him about my feelings but I also don't want to ruin a friendship if he doesn't think of me that way. Should I open up to him? (I have no idea if he is happily married. My husband and I have always had an open relationship..though this is the first time I have felt emotionally attached to another).