Dealing with an 'open' relationship?.

Ok so I pretty much fell in love with the man of my dreams just under 2 years ago and from the first time we met, we stated that we didn't want any secrets between and it wouldn't be a strict monogamous relationship (we both believe that people aren't designed to be monogamous).I am happy for him to have his freedom as long as he isn't doing anything that will affect us as a couple (screwing random guys from those 'apps' or arranging anything when we are supposed to be together or finding out I have an STD from him because he was doing stuff with others). We don't live together yet as we love our own space to much (but do spend the entire weekend together) and since we became a couple I just haven't felt the need to play with anyone else, where he been with a few other guys, they are all guys I know of and have just been spur of the moment things. He has always told me when and what happened.In previous relationship I have always been the one with the lying and the sneaking around which is why I have always said as long as there is honesty between us then its ok to play.But every time he does, I start over thinking the situation and my brain goes off on a tangent thinking about anything and everything. I know in my heart that our relationship is about as solid as it can get, I want to spend the rest of my life with this guy, I love everything we do together, we do all the normal couple things and I love that.So my question to you lovely people of this sub, is how can I stop focusing on the non-existent negatives that I make up in my head when he does have fun, at the end of the day that is all it is.... fun.I suppose I should mention that I have quiet low self worth, I will honestly never feel like I deserve to be with such an amazing person, mixed with some body dysmorphia (I really don't like the way I look body or face wise, but yet ironically enough when I play with myself I love doing in front of a mirror lol)Anyone else in an 'open relationship'? Although I don't consider it 'open' its just more if the mood takes you kind of thing.