How hard is an emotionally open marriage?

A quick update

Sandy and I are taking a short break from d/s. This includes orgasm denial (though it pained her to say it) and denial of intercourse. We are also in the last make or break stage of keeping this marriage open with this lover,  stopping the experiment. 

When things settle I hope to write much more about it. Hopefully it will settle without us having to stop but we are a hair breadth from that decision. It is proving very tricky to manage a three way relationship. This isn't pure sex or friends with benefits. Sandy is naturally prone to immersing herself in her lover, at least for the first months and flush of excitement. He is emotionally demanding and unfortunately has fallen in love. Love is fine to a point, but he is constantly trying to get her attention and is jealous of me. she can't easily keep away from him mentally and reserve time and attention for me partly because of her own excitement, but more because of his possessiveness and constant contact. I feel he is a threat to us, I am trying to be open to sharing, he is not. As a result I was starting to feel jealous of him until realised that this is not the way it should be, that were he not so demanding of her it would be more lighthearted and fun for all, and not feel so threatening. 

Sandy is stressed at work, tired, busy. She has not got the time and mental energy to deal with that, and me, and kids, and work etc. She cant see him several times a week and still have time and energy for her family, or be responding to texts in the evenings instead of being present with us. 

She intends to talk to him about this tomorrow. I have my doubts he has the maturity to cope with such a complex relationship,  if he doesn't it will end soon. 

For my part sandy has said that she wants more freedom, is not comfortable with my being too involved. This is a learning experience for me too, and in principle I am happy, both as a husband and a sub, to set her free. I hadn't realised she felt that way.  We both agree though that we need to think about how it is working first. I have taken more control since we started rather than less because I don't trust him to respect our marriage, and because she has made some serious mistakes that have hurt me. It is a learning experience for us all, and a hard lesson. She sees why I am like this. I see why she did what she did. I love her and know her, I can understand her actions and am beginning to understand her needs and drives. 

We are doing some hard thinking the next few days. Much will depend on him, she and I can make it work we think, though we aren't sure, but can he?