I've already posted this in a similar thread but here is what worked for me when the propose option wasn't showing up:
1). Close the game and restart the phone.
2). Click on the sim you want to propose to.
3). Scroll down through the options to see if the propose option is at the bottom of the list. (It sometime is but usually isn't)
4). Check all of the options, start with all options under Romantic (Flirty)
5). If it isn't there check all of the options under Rival
6). If it isn't there check all of the options under Friendly
7). If it isn't there check all of the options under romantic (again). For some reason this is when I usually find it.
