Because I have several couples I want to get together and its taking ages. I've tried almost constant romantic interactions and nothing. I've used TestingCheats and moved the relationship bar but that just made them best friends. Is there any cheat or mod that will make them in love?

Maybe they just don't work as a couple? Not sure if the game has a system that works like that, but it could be a possibility?

Just keep socialize with romantic interactions like flirt until sim feeling irresistible or something like that.

But I've spent almost a real life day doing that, I'm not convinced its every going to happen. It could be because they are not compatible. Is there any kind of mod to overide that?

It's -weird- that it wouldn't work if you're just doing a bunch of romantic interactions - are they always getting + or ++ when you do? Make sure you're varying the interactions too - not just flirt - flirt - flirt but various different ones, without having two in a row the same or doing too much of any one. Any two sims should be able to eventually fall in love that way - if they have massively different personalities or one is unflirty, they may take longer to do so, but it should work eventually. Do you have any mods in your game?

I'm pretty sure Twallan's MasterController allows you to alter the relationship between two sims.

To actually trigger Romantic Interest (which I think is your problem) I believe they have to either "Confess Attraction" or "First Kiss".

What I normally do is use a trait specific Friendly Social, alternate that with enthusing about the other Sims career to spam the ++. Once they become friends (which I find to be the minimum level that "Confess Attraction" works) I go around the romantic pie chart - Compliment Appearance, Compliment Personality, Flirt, Flirtatious Joke, Amorous Hug. That normally gets them to "being very alluring" and then "Confess Attraction" followed by "First Kiss" then I hit them with a Massage, and another kiss, then Make Out and by that point they are normally ready to Woohoo

It certainly does. You can set relationship status to be in a relationship, engaged, married, etc. I would vote for this being the quickest and easiest option if you want your sims to be together.

Get the "Never Dull" reward on one of the sims in the wanted couple and spam whatever is your quickest social (I use Salute) until they have a bit of rep, then spam flirt until you get the thing saying "Extremely Irresistible", and then either select Confess Attraction or First kiss from the romantic menu.

without using cheats, with generations out it makes it even easier. you have to at least be friends. and like severedsolo said i start with a few friendly options first.. ask about day, chat, get to know. then you can use "pick up line" if they've never flirted before. and ensure that they arent already in a relationship bc if they are you have to have the relationship higher. but if they are single, pick up line, then flirt, and maybe a compliment. then i give flowers. and you promptly go to "alluring". you should then be able to click on confess attraction and first kiss. i usually have a prospective romantic interest meet out, b/c then i tour a building and have them make out. and after that the romantic options are all unlocked. and whats even better than the "never dull" reward is the "master of seduction", b/c then all romantic actions are accepted.

I just do this. First, I make sure they have the "romantic interest" relationship type thing. Second, I enter the testingcheatsenabled true. And last, I drag the relation bar to the full in the relationships panel. And when you use romantic interactions toward that sim, they seem easier to marry and wohoo and stuff. Well, to me, that is. :P

I find it the quickest with the combination of 'Never Dull' and 'Master of Seduction'. This will allow my Sim to repeat romantic interactions over and over again without fail, and he/she will never be rejected. I managed to seduce Richie Striker in a day and made him divorce his wife, and my Sim is already moving on to another boyfriend.

From what I've read, if you've progressed to "Best Friends" you CANNOT get romantic... apparently their are some friend-zoned nerds at EA with a grudge to grind... So you have to do something to lower the relationship and lose the best friends status, then focus on romance instead of friendly.

I don't know where you read that, but it's wrong. My Sims are always getting romantic with best friends. My kid Sims "Talk to Friends" constantly at school, and then get jiggy with them at the weekends, by which point they are often best friends.

Select another household -> host a party, invite the wanted couple -> convince to kiss
I always use this on Bella and Goth, but they always end up splitting up and die along.

new shoes, big car and an expensive bottle of nectar does it for me ...

WAIT... WHAT? I didn't know you could do that! o.O

Anyways... no idea why they won't fall in love, what i do with my sims is use the romantic interactions like "kiss, make out, hug, hold hands, flirt" and stuff until they fall in love... keep trying different romantic interactions, also, try being friendly before, that increases the chances... just like in real life, LOL!