Hi! 
i am only 2 days new to this game. In the game I have a steady relationship with some one for 3 years. i just wonder, if it/s possible to get married or engaged with this person at some point? And yes, i did check th eprevious post of marriage but I still don’t get what is a " deeper relationship" may occure. 
I’m afraid there’s no engagement or marriage in the game. maybe in a sequel… (if there was a sequel, definitely it would be in there).