I got the Ultimate Collection back at the end of July, and over the past week, have been playing through it. The only mod I currently have installed is the one that changes the initial loading screen to the Ultimate Collection logo, nothing that should be effecting actual gameplay.

The sims in question are in love with each other, have high chemistry (two lightning bolts), and I can take just about any romantic (or lustful) action on her, but I'm not seeing "Get Married" under the "Propose" option. Instead it only shows "Move In" or "Stay the Night".

I've read through this, and haven't found what I'm doing wrong: http://sims.wikia.com/wiki/Marriage

Have you got them engage yet.

In hood view type in the "boolprop testingcheatsenabled true" and then go into there house and while both sims are on the lot use "shift click" on the mailbox and one of the options should say "set pregnancy relation with" and chose the sim and you should be good to go.

No, I'm trying to get them engaged.

That's weird, did you create those sims or are they from the game? Have they been resurrected, previously married? if they are maxis sims, have you checked their hands for any existing ring (you never know^^), basically, who are they (if of course they aren't both custom sims you made yourself)?

I only made one custom to play as, I figured the rest I'd just interact with in the world. I didn't think she'd accept a date if she was already married, I'll have to check that next time I play.

Sims aren't monogamous by default, so yeah, it definitely sounds like it'd be a good idea to make her selectable and check that she's not already married, that she's also in love with your sim etc.

Sims will indeed accept dates if they are married. Check her hand for s ring, also what's her name? If the sims have a high relationship score the propose>get engaged should be there if she is single.

I had my sim invite her over for the sole purpose of checking for a ring. She brought over a "friend" who happened to be her husband.

After that I tried the matchmaker, and there was a glitch that caused the girl on the date to stay in the house even after the date was over; I couldn't ask her to leave for some reason, even though their relationship was only good friends at that point. I tried evicting my sim and immediately moving him back into the house, but that cleared the house of all items, and I didn't have the money to buy them back (not to mention rewards and crafted items)...

I'm going back to Command and Conquer for now; I'll probably revisit Sims 2 sometime in the future.

Thank you to everyone who posted in this topic. Feel free to lock or delete it if you do such with solved problems.