Experience Tumblr Like Never Before
I was thinking ONE of the reasons why Tenma could've stayed with Eva for so long and put up with it was because he was scared.
Cuz the moment he graduated highschool, he left Japan for a foreign country (according to Another Monster). So of course, he was very young, that's a scary thing for a young person. Sure, it's not like anybody had his back in Japan (cause his family were a bunch of opportunistic rats) but he had people he knew, and knew what to expect, and now he's in a whole other country with people who can be hostile to him for being asian, since at the time they didn't take kindly to foreigners/minorities.
He made friends in college but based on how he is (in Another Monster, it is said he never liked being in groups), he probably didn't feel like it was actually meaningful since none of those friendships lasted. I feel like people were only interested because OMG ITS JACKIE-CHAN!! joined their white-dominated college.
Really, the only person he could rely on was the director Heinemann and Eva.
He put up with it because he needed someone to depend on, he needed someone to guide him and tell him what to do just like Eva did, because in the end that is all he had. So the poor thing, of course, would be scared to be left without the things and people whom he relies on, even if those things harmed him.
He was young... Only when he grew up and was able to live independently, he was able to let go of those things, after he's had enough.
All the people he's depended on wanted nothing but the worst for him tbh </3 maybe that's why Eva's curses never phased him cause he was used to it already due to his bitch mom (unreasonably harsh on him according to Tenma's former colleagues. I'm 100% sure it's worse than they put it cause Tenma is the most patient and forgiving person ever, his family and stupid mom must've been the worst if he literally never went back, never responds to his brother's letters and overall does not wish to speak about them).
I could go in more detail about my headcanons for this but I'll see.