Immigration in the US?

No, they won't come looking for you. However, you can never use the Visa Waiver Program again, not in this lifetime at least. You cannot adjust status either. So, if you marry a US citizen it will do nothing to get you legal. You'll have to leave the USA to make any attempt to become legal and that will be problematic for you.

The moment you leave they will notice it and you will face a 10 years travel ban because of this (good chance that they will never let you in again, because against popular believe there is no guarantee that even when the 10 years have passed that they have to ever let you in again.)

btw. good luck getting a visa (if you don´t need a visa there is still a chance that you will be turned back the moment you try to enter) for any other country again because many countries share this kind of informations.

This is not a good idea. if you like America so much why not apply for citizenship? It will be very hard for you to get a job and its going to get tougher if you are here illegally.

when you try to board your flight home you will be arrested and get a 10 year ban from coming back . it will not be fun at all

No but you cant get a job