Advisor threatens to discontinue fellowship. What should I do?
This is a tough one.

To be brutally honest, from your post I can gather that your English is not up to scratch for English language journals. And that's not a minor issue.

Thing is, it's not your supervisor's job to fix your English mistakes and it's not ok to keep giving him draft over draft over draft. Academics are super busy people. And if you want a paper published it has to be free from English mistakes. No-one is going to fix that for you.

In regards to the rejected paper, four rejections is a lot. It shouldn't take more then 2 revisions to get it accepted. Do you fully understand what the one reviewer want fixed? You need to fully address the issues the reviewer raised, otherwise you won't get it accepted.

Having said that, if you've done enough research for five papers, you've done very good work. It looks to me it's your English that's holding you back, not your research.

Can you get help with English from someone? Don't rely on software, that's not going to fix it for you. Can you afford to pay someone to fix it for you, there are people you can hire to proofread? Can you take a 3-6 month break and do an advanced English course? Is there someone at your university you can talk to?