Would like to know more about Mexico City

Strange question: you need CONVINCING? That is beyond the responsibility or capacity of any person replying here, plus you say nothing much about yourself. It is your decision. If the relationship is of primary importance in your life, that is a reply in itself - but your partner did not consult you??? Strange!! Where are you in California? It is a wonderful place to live, in general! Mexico City is  a very large city, very cultural, international, sophisticated, but also very costly, polluted, with gray buildings, lots of new development etc. There are charming areas too of course like Coyoacan but, again, it is not cheap to live in the nice areas, and generally English teachers are not paid well, in the language schools at least. You might find a better corporate or university position, depending on your qualifications and of course the availability of a post. It would be better to visit first. You sound scared, that is normal, but it would be a new enriching life experience - and Mexico is wonderful to explore! It is really up to you....and professional opportunities....