Hi
Glad your still alive and sorry you and Izzy cant work things out. I hope it gets better between you two

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As for the other stuff. The super teching of the AI sounds like you playing a game that allows tech brokering. That means the AI's are gonna trade with each other left and right. I bet even some of the nice deals you made with your boyfri..err oops I mean "vassal" (hehe j/k

) are probably being regifted all over the place too. So that means they can all go down diff branches of the tech tree then trade with each other and not lose ground.
And as for happiness. I am not sure what going without more info. Like do you have a state religion and temples and collseums and theaters in your big cities? How many happiness resources do you have? Depnding on resources even buildings like markets and forges can help. In addition to boosting gold and industry they also give extra happy faces fif you have certain resources.
Also if you have access to more than one religion and havent been spreading around your non state religions that can help a little too. Then you could build the non state religion buildings too for a few more happy faces. Only big downside to this route is IF your state religion is also the Apostlic Palace religion then spreading around nonstate religions will dillute the amount of votes you get. And if you go to war with civs that have the holy city for the extra religions you spread that may cause some unhappiness in those cities you spread it too. But only while you at war and if you capture the holy city then it goes away.
Also a couple of happiness resources go "obselete" when you researche certain techs. Like ivory and whales with combustion and fur with plastics. So if you were getting happy faces form say ivory and then reserched combustion you will lose those happy faces. So that can account for sudden increase in unhappiness too.
Also if you using a leader that gets a happy face from having a monument in a city, when the monument was obsoleted by scientific mehtod you lost that happy face in those cities too.
Scientific method also obsoletes monastaries so any science you were getting from them got dropped once you discovered that too.
Some wonders that help with teching by giving extra trade routes and stuff also start getting obselted once start getting certain industrial age techs so any thing like that you were using might have been lost now too.
If you have collseums and theaters in your cities uping the culture slider will also give a happy face for each 10% culture you go. Since you haing trouble keeping up with tech it might not be good idea to lower your tech rate. But if you can lower your gold or espionage 10% or so it could help to do that then up your culture.
Also what civics are you running? Representation give plus 3 happy faces in your 3 biggest cities AND makes all your specialists in any of your cities give an extra 3 thingies of science per turn. So if you are not using that civic switching to it would help your happiness in your three biggest cities AND help your science. In fact if you were using representaion and switched to something else THAt could also account for sudden drop in tech and happiness.
Also remember that farther you go in tech tree more expensive things get so number of beakers that was fine in classical and rennasance might not cut it in industrial age so if you havent been keeping up with putting in all the science buildings you can in your best cities and maybe even an academy or two then even if you havent lost any beakers at all your tech rate still gonna slow down unless you work to keep your beakers per turn increasing the farther you go into tech tree.
One final thing. Your citizens do actually tell you why they are unahppy. Just go to city view and hold pointer over the smiley faces at the top. Then they will give you a list that breaksdown all they things that are accounting for each happy face and each unhappy face. The unahppy faces should JUSt all be for the reason "it's just too crowded". If you;re at war though some may be "war what is it good for? absolutely ntothing..ungh" to aco**** for war weariness. If you get reasons like "the world considers you a villian" it's because you defied a AP resolutions and if you get "we have been told about your villiany" or something like that it means that city had a "insite unhappiness" misison against it.
So that can give you an idea of why your cities are getting unhappy.
And besides represntation other civics can help happiness like hereditary rule will give one happy face per soldier garrisoned in the city so if you have lots of soldiers in your cities switching to that could help the happiness. There might be other civics that help happiness too like one I THINK that gives extra happy faces per barracks when you use it. I cant rem off top of my head since I mostly stick with representation as soon as I can get it. But look through the civics and see which civic combos would give you most happy faces and then decide if getting them might be worth switching to em.
Well anyways that all I can think of right now. Sorry it isnt more but I hope it helps a lil bit
Kaytie