Would you go from an open relationship to a monogamous one? Are you 100% happy in your open relationship? Have you fallen for other people?

I am not in an open relationship or considering one. However someone I was seeing was in one and I was not clued in on that important detail before being involved (which was not okay, but not the point) they were a close friend to me and I developed strong feelings before knowing that it was not an exclusive thing between us. We kissed and went on "dates" and were a little physical but did NOT have sex. He shared a lot of emotions and feelings for me and was the one who initiated. He claims he did not tell me because it turned from something casual to something real for him and knew he would have to end his current open relationship to be with me and was unsure about it all. (Not sure if that is entirely true, but that is what he said)
I am not trying to disrespect the situation, just looking for friendly insight.
Have you ever fallen for someone outsife of your open relationship? Is it normal to be emotionally involved with others or is it usually just sex? Is it odd that he treated me like another girlfriend entirely? Have you switched between open and monogamous? Are you 100% happy being open? Do you feel very in love with the person you have an open relationship with? Or do you just like and care for one another enough to date but also see other people? Do you usually tell orhers up front that you are in an open relationship? Do you think the feelings he expressed to me were fake or to "woo" me more than they were real? Again, I did not sleep with him and expressed that I don't sleep with people right away and it would be a long time before I felt ready for that, so I don't think it was all about sex- but could be wrong. A lot of questions, but would appreciate any insight or opinions. Also, what "rules' do you follow in your open relationship?
Thanks!
Would you go from an open relationship to a monogamous one? Are you 100% happy in your open relationship? Have you fallen for other people?
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