For a long time, he hasn't been picking up phone calls, responding to emails, or completing tasks that he agreed to do. Sometimes he'll send a text, like seven days later, asking for a clarification on a requested-task that has now already been completed.
Things are finally starting to pick up. I don't know what to do. Technically he owns 50% of the "venture" but it's not like we've issued stock, etc. Things are hairy.
Its one way to avoid the deadlock situation where one founder mentally checks out, offers no value, but refuses to be bought out at any reasonable price.
How would you prevent a founder from bluffing though? Say founder B knows that founder A only has $X, so he offers to buy it for $X + some number. Makes it hard for founder A to keep any ownership of his company without taking out an expensive loan and paying way more than the company is worth.
Their actions show they're either unwilling or unable (due to other commitments?) to keep doing the hard work of being a founder, no matter how much they might still like the idea of being a founder.
If you're lucky, they're aware of this, or can be made aware of this. Maybe they've only been sticking around out of a conflicted sense of obligation. "I can't just leave them in the lurch!" (nevermind that's exactly what they're doing by their actions, good intentions be damned.)
A buyout offers them an out.
If you're unlucky, at worst they'll probably want more money.
Best of luck!
My previous company with two 50% cofounders had a provision, where in case of an unresolvable disagreement both parties would make a blind offer to buy out the other party, and the higher offer wins.