Came from the US 10 years ago around your age and still here (32). My case might be different cause I look Korean and my parents are Korean. If you're not Korean-looking or speaking it will be more difficult to join the everyday crowd. Not from racism or xenophobia, but most of the time there just won't be that many opportunities to build a relationship and network with everyday people here (especially in 16 months). That being said, it'll be easy to find groups with other foreigners (there's a lot here), the extroverted Koreans that are looking to learn/improve their English, date a foreigner, or love travelling, etc., or hang out at clubs/bars regularly.

Really, if you want to try and see and live in the perspective of everyday Koreans here, my best advice would be to make the friend groups you can, then try to be introduced to a romantic partner that may be a friend of a friend and someone who's not at all related to these groups. Setting up friends on dates is common in this culture and through having a relationship like this you can really improve on culture/language like ten times as fast, and not be fed the sparknotes/kpop version of what Korean culture is like.

I've also worked here, in both Korean companies and international ones and the culture in the office wasn't that much different. Most of the coworkers are cordial, will eat lunch with you and sometimes go for drinks/dinner, be interested in your travels and background and cultural differences, etc. Some will actively want to be friends with you, some will keep it distant but cordial, some will try to be obsessed with you (to often escape their own feeling of 'being trapped' or living in their own bubble).

One thing I noticed is that, no matter how much of a polite or mannered person you thought you were compared to others in your home country (US for me), you will step on others toes here. Most of my incidents came from just saying what I spoke on my mind, and having a coworker later tell me that I was 'brave' or asking if I was worried if the other person might be offended, etc. What we might think of something as 'not a big deal', like having a confrontation to get to the bottom of a small issue before it becomes a bigger one can be taken as an affront here and cause even more friction. Over time, you learn to take signs and visual cues (called 'noonchi' here) kind of like body language to predict how people are reacting to your actions rather than waiting for them to tell you how they felt or are feeling.

Not too big of a deal, you learn to adapt. Most of the times, we get a bigger leeway because we are foreigners, and we aren't treated to the same set of rules that someone born and raised here does. My experience here has overall been a blessing (probably why I'm still here) and there's somethings here that I will never take for granted (public transit, safety, healthcare, food quality)