It sounds like you own 40% of something fairly valuable and now that it's 11 months into your contract other founder who needed your help is getting greedy and trying to push you out before you are owed anything. You said it yourself, you've grown hugely, you're dominating SEO since you joined, and built loads of products. This is your 'partner' getting greedy after you've done a lot of hard work. It wouldn't have ha…
Go scorched earth - what do you have to lose? Know the other guy is hostile and don't trust them to do the right thing. Consider your options outside of that and talk it over with the other investor.
If you're the technical cofounder here you're probably in a stronger position to negotiate.
If you can get the other investor to see what's happening here (your cofounder pushing you out one month before the cliff after you've helped to build things up) you may be able to get them on your side.
As I see it without knowing details:
- Either your contributions are real and your cofounder is a miserable person trying to screw you out of it and risking the company in order to do that.
- Or you haven't done anything substantial and the cofounder wants you out. Even in this case it's still wrong of them to do this one month before vesting (and the way they're approaching it sounds dishonest, they should be direct).
If it's truly the former I think getting the third investor to understand this is key, if the non-technical cofounder is risking the entire business at this stage they're going to be bad going forward - you probably need to get rid of them.
If it's the latter (which seems unlikely since the other cofounder is non-technical) you'll still want to negotiate a reasonable exit, but it may be harder to do so (and you'll probably need a lawyer).