Want to end marriage but too scared

We will be at 15 years of marriage on November 17th and feel like I am trying too hard to make this work. It hasn’t really been good for a long time. I thought it was better to stay together for the kids. I thought about planning an anniversary dinner despite all the ups and downs and disconnection but I’m kind of tired of trying on my own. I think we want different things and am annoyed that I’ve let it go on this long but that’s not helpful. I honestly don’t know what I should do but know I’m not happy with the way things are. It would be easier to work towards retirement with this man but also makes me so sad to live life settling. I’m unsure of what to do but I realize I either need to change my thoughts or the circumstances.