Well, the thing is, if you do something for a living that you love to do, the odds that you will get bored or sick of what you love to do, is not likely, since its what you love to do.
When I was in my last year of high school, I heard and saw people around me that were working for a living and alot of them were always unhappy, or hated their jobs. Most of them hated the idea of even getting up in the morning and going to work. I thought that if I could do something for a living that I loved to do, then that would make it easier to go to work and also enjoy working, since I would be doing it the rest of my working life.
Well, I found that thing and for me it was being a software developer for computers. For me, I loved the aspect of writing programming code and seeing the result happen on a computer screen. I get to be creative and that is what fuels my desire to keep doing it. It gives me such a thrill.
I am also a musician, and I love doing that, but I don't think for me it would be as reliable for monetary income as my software job is.
I have done my software job all my working life and I never get tired of doing it. Yea, I have worked for some lousy companies I discovered after awhile, but I never got tired of what I did for a living. I always and still do look forward everyday of doing my job, whether its for one company or another, I still get to do what I love. To me, you can't beat that. To get paid for doing something you love to do, is like the idea job. I don't look my age and I attribute that to not dragging myself down emotionally because I hate my job or I can't stand going to work everyday, which is what could make you age early in life. So, if you choose to do something for a living that you love to do, you will find out you are going to be better off than if you choose something to do just to get by. You may have to make adjustments along the way, but overall you will still be happier.
As for the hardships of being an English Teacher, I can tell you that some of my best friends are actually school teachers and its not an easy career. Its not even about being an English teacher, but just any kind of teacher. If you are talking about a teacher position like in a school, there are always situations there you come across, whether its uncontrollable students, or the the school has issues in the way they handle things, or you get laid off because of what ever reason and so on. Now days, schools are nothing like they used to be when I was young. These days you never know whats going to happen when you go to class. I personally would not be a teacher in today's society. Of course I am speaking from the context of being in the USA. Maybe schools abroad in other countries may be better, but what I see happening in schools today, frightens me. That's not to say we don't need teachers, we surely do, but a person who wants to be a teacher needs to be a special type of person to be able to handle today's standard of students. I give Kudo's to all people who are currently teachers.
Good luck to you in your future endeavors.