The Sims 3

Okay so to start off you create a new game and make two Sims (male & female adults) and put both of their Traits as:

-Flirty
-Charismatic
-Great Kisser
-Hopeless Romantic
-Friendly

And set your relationship status as 'House mates'.
Move them into a house it doesn't have to be any specific house. [Make a New save right there!]
Let them talk for a little bit until you unlock the options to Purpose & Marry.
Once you've done them both with the one Sim you should have 2 of 5 done at this point so Make another 'New' save but NOT over the previous save.

Quit and Re-load the previous save where you first saved after just getting the house and do the same again and like before just save over the Other save (not the one where you just got the house). And same again just reload and after the third time doing this you'll have the achievement unlocked within about 15 minutes at most! :)

Hope this guide helped, If I've missed anything out please leave me a comment so i can add it in the solution :) thanks

For this achievement your sim/sims are going to need to start 5 romantic relationships. First let's identify what counts as a romantic relationship. If you get to the girlfriend stage with another sim that's one. If you go on to marry that same sim then that will count as your 2nd romantic relationship. So as you can see that you can get 2 romantic stages on 1 sim.

Now that you know how to the relationship system works you need to know how to get a romantic relationship. You're going to want to use the same tactics you used for the achievement You Never forget Your First. Start them off slow with conversations and maybe even get them into the friends stage. Then start going all out on the romantic conversation options like flirting and hugging. Eventually you'll get the option to kiss and that's when you know your on the right track. Keep continuing to use romantic conversation options and then once she thinks you're extremely irresistible propose to her. If she says yes then you should have 2 relationships out of the way. Now you can either be mean to her and kick her to the curb with a divorce or you can get the other romantic relationships with other sims. You can use as many sims as you want for this trophy. You can check your progress by going to the challenges menu and searching for the "Matchmaker" challenge. Once you get 5 romantic relationships you'll unlock this achievement. The following traits/lifetime wishes can help you obtain this achievement.

-Attractive - Lifetime reward
-Flirty - Trait
-Charismatic - Trait
-Great Kisser - Trait
-Hopeless Romantic - Trait