How do you break up with someone?

Been with a guy for 4 years. We were living together until he quit his job in November. Since then we have seen each other a few times but talk everyday, multiple times a day.

I let him borrow my iPad a few months ago and needed it back for school. He left his IG logged in and I snooped and found he's planning an overnight trip to Vegas with 2 female friends "under my nose".

He told me the day the discussion happened that he was going to hang with friends the weekend of the 23rd. Then I saw the messages on his IG. Today he messaged in the group chat he might leave the group in case I come over. So he's definitely trying to keep me in the dark.

I have not confronted him. I tried to get him to tell me about it by asking about his friend and then what she was doing for his birthday... He straight up lied to me. How often has he lied to me? Do all men lie? This is a big one.

I am trying not to turn the breakup into a big fight, I just want to bow out. I have stuff at his place and I want to make sure I'm not leaving behind valuables. I also have a cell phone plan with him...

I just need advice on HOW to break up with him. I have never broken up with someone I still had feelings for. This lie is unforgivable and all the crap I've let go is as well. He's just not a solid guy (do they exist?).

Thank you.

[Edit] I'm not sure if it shows I edit or had to say it... He lives with his parents. I was thinking of maybe just driving out there (he's 90 miles from me now) when he's at work and going through boxes to find my stuff and explaining the situation to his mom. Crazy?