You just do it. I know, not helpful, so I will break it down.

First, assess what you share that you need to deal with. If you have stuff of his to return, if he has stuff of yours you want back, if he has access to your money or keys to your place. For the latter items- change the passwords/get rid of accounts he has access too, and try and get the keys back a day or two before you break up with an excuse (friend is stopping by so I need to give them the spare). Also take this time to collect your shit- quietly- from his place.

Second, break up. Go to his place, with his stuff, and break it off. Keep it short and simple "this isn't working for me, as we discussed X, Y, Z, and I am ending the relationship." Now, this is where it gets hard, because he is going to argue with you, and you simply do not participate. I learned this from a boss about firing people; you have made the decision, you don't need to justify it, you don't need to prove them wrong. Let him say what he needs to say- within reason- and you simply nod and show empathy, and end with- well I disagree and have made my decision. Sidenote: If you worry he will be angry/violent, break up in a public place instead where you have your own transportation. A walk in the park or a beer garden is good for this, not a restaurant where you have to wait for the check! Coffee shops are okay but sometimes can be very quiet. Basically, a public place where you can actually have the conversation without feeling like you have an audience, and where you can escape.

Third, do not respond to attempts at communication. You don't have to start out by blocking him, but you need to commit to "I need full space apart for awhile before even figuring out if we can be friends." If he texts you about very practical things- do you have my hoodie- you can respond and keep it brief, no small talk, solve the problem, end convo. If he starts harassing you or you think you are caving, then you silence the convo or block him. I find blocking hard because I worry it was harsh (I liked this person at one point, they weren't abusive, it just didn't work out), so just control your responses, don't get dragged in to conversation, and ask him to stop or you will block him if he is like bombing you with "i miss you."

Fourth, sorry you are a woman. Because of that, I have to tell you the following: Besides breaking up in a public/safe place, you also need to be careful for the few weeks after breaking up. Maybe stay with a friend/family if you live alone or have someone stay with you. Vary your schedule a little if you can (aka, you always leave for work at 8am, maybe go in early and get coffee for a few day). Always be very vigilant of coming home and leaving home, same with work, school, or other places you frequent. Some of this is good breakup advice regardless of safety- go visit friends in a city over, have a slumber party and eat sugar, stay with family- and yes, is this all a little nuts? Sure, but it is better to spend two weeks being a bit paranoid and then laughing it off than it is to be...on Forensic Files.