This is a really easy one to accomplish, not sure if you can do this with a couple that are already married or not - but for simplicity I found a person living alone in my default neighbour's town and sent over one of my Sims to make friends, after that it's just a matter of keeping on being romantic until you reach the dating stage.
You probably won't need to find a friend playing the game also to complete this task as it is really easy to do.
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