That's kind of the point of his character arc though. He's a broken man. He's suffering from pretty severe PTSD over what happened to him, and the very thought of forming another professional partnership with someone is just more than he can cope with.
He loves Kindra (friends or otherwise), he would give Kindra his work and labor for free but he doesn't fully trust her yet, because he just can't. Not that he doesn't want to, not that he thinks she's untrustworthy, but because the trauma he suffered prevents it. The thought of opening himself up to fully trusting someone with his work again triggers a severe negative emotional response.
So long as he's just a worker bee, providing her labor he can't really be stabbed in the back or let down. If she fires him, she fires him. If she takes his work and doesn't credit him, well that's what companies do. But if he were to partner with her, fully trust her, and then she were to do either of those things? He probably wouldn't recover from that.