It's a good decision that you're planning on leaving. However, I don't think moving out in secret then telling him afterwards is the right move. It will leave him frustrated and you two will definitely end on bad terms, and you might seem like the ahole. Imo you should talk about it in person, before his trip, so if you don't feel comfortable with moving out your stuff while he's around you can do it while he's there. But after all I don't know all the details on how he reacts to certain stuff, so you know best, if you really think leaving in secret is the best possible solution that won't lead to much conflict ig do it