You can be insecure and scared that your partner might fall for someone else in a monogamous relationship too. And it can happen in a monogamous relationship too. It can happen everywhere, at any time. Your partner can meet someone else at work, on the street, while buying bread, at the gym... I mean, security or insecurity is inside of you, it doesn't depend on what your partner does.
From my PoV, imprisoning your partner and forbidding them things is not a solution to your own insecurity. Many relationships I see out there are not based on love, but on fear and dependency. They say they're in love and explain their monogamous relationship this way, but when you truly love someone, you want them to be happy, don't you? Is forbidding them things and treating them like an object that you own a good way to make them feel free and happy with you?
I don't know, that's just me. Maybe that's because I tend to be in love with several men at the same time. Maybe that's just a naive ideal, but I think you can be really committed and there for your partner while seeing other people or having more than one relationship.
I never had an open relationship, but I had a double relationship once. I mean, two at the same time. I wasn't cheating, I asked both guys if they agree before doing it. One of them had no other relationship, and one of them had another girlfriend. When she needed him, I didn't mind him staying with her. If one of them needed me or had a problem, I was there no matter what. Being there for more than one person is not a big deal. I do that for all of my friends too.
Plus, when you have two partners it's not necessarily the case that these partners never see each other and hate each other, so that you have to choose whom you will see. You can spend time all together. Peace and Love
