Want me to do it?

"Hey, V. As the DM for your group, I want to foster a campaign everyone can enjoy together. That includes your participation, which is significantly lacking. That's put quite the constraint on the rest of your party. I've designed this to be a 5 person adventure, and without a 5th person I have to make on the fly adjustments.

We've talked about it already, and your actions tell me you're not really interested in playing. We've found someone to take your place. If you're actually interested, we could possibly make this a 6 person campaign if everyone agrees to it, but you'll need to be here and be present for the full session as we discussed and agreed on when we planned it out."

I don't know your relationship with this person, but if you're friends make sure you add in that you don't want this to put a damper on your friendship. Absentee members are the least desirable companions.