Would a ford focus 2012 with 80k miles last a long time given that i treat it right and only take it within the city from and to work?

As long as the car would last me 5 years minimum
but i don't know jack about cars so if i could have an expert give me a diagnosis i would gladly appreciate it

So i have a 2013 ford focus with about 80k miles on it and it runs great. But you have to make sure you keep up with the maintenance required on it. You can find that by simply googling "2012 ford focus maintenance schedule" and don't take it to the dealer. They will rip you off on the cost. Find a local mechanic for those maintenance check ups
Also a car should last you more than 5 years. More like 10-12

Yes, it could easily last five years if you take care of it.

If you have one with the DCT then I wouldn't count on making it 5 years trouble free.

"so if i could have an expert give me a diagnosis"

Fundamentally speaking, if the car doesn't have a problem currently. Then there's nothing to diagnose. It would be like going to the doctor when you're perfectly healthy and asking him what's wrong with you.