I'll make a few general comments on this game from a quick glance, as it is late and I'm off for the big snooze. I would note that it is a bit harder for folks to improve your gameplay in such late stages of the game, but there are some things we can I assume and some things are quite obvious.
1) As for diplo, my take is you don't work on this aspect of the game much at all. Granted you have attacked some AIs that some other AIs have liked, and you get maluses for that, but still there are a lot of things you can do starting even very early to nurture your relations. First, you barely trade resources with the AI (granted, I do note that you have a stop trade with Joao for some reason). Resources trades benefit you either in more happy/health, but also gold. You should always trade extra copies of resources for something, and possibly even single copies temporarily if not immediately needed. You will build up to +2 relations over time - faster the more resources you trade. I'll touch on civics next, but note that two AIs have fave civics that are good civics (and well, since you don't have CS, Vassalage would do you some good too). Tech trades, of course, will help with diplo and the more you trade or gift techs you can hit a separate bonus besides the fair trade. I see some rejection of demands or requests - always ask yourself if it is not a big deal to just accept a demand.
Now it is important to mention that you often do have to pick sides here. Because of peaceweights and religions, and whatnot, sometimes a leader is just generally hated, but you should always try to foster allies (even if you kill them later), and you can start nurturing this as soon as you meet them.
Also, you have like no open borders with anyone.
2) Civics - I've no clue what your overall tech decisions were over the course of the game, but neglecting to tech Civil Service early is a major major mistake. CS should always be a priority for the human. Bureaucracy is the second most powerful civic next to Slavery, and you have a very nice Bureau cap, that should actually have more developed cottages (and no forests at all..those would have been chopped away very early). Seems you went through Theocracy to Paper/Education. Theo is not something worth teching generally (granted you might have traded for it or received it in a peace deal, but neglecting CS is very bad). CS is something you want to have in your pocket before or circa 1AD.
I'm honestly just plain baffled that you are not in Representation. (can't remember if you built mids or captured it, but even so you should be in at least Hereditary Rule) And Free Speech is a bit odd too, granted you don't have CS.
3) Looks like you mainly just like to build buildings. Only building a city needs is a granary - the rest of the buildings are situational. Why is Susa just now building a granary? Walls? Despite being something a human should never build except in emergencies, at this point in the game they are useless and basically obsolete.
4) You are almost certainly going to get DOW'd by Boudi (and Alex who you should have killed or vassaled) and Peter, probably very close to the same time. I don't see that going well for you, although cannons will help you a lot. Problem is you are barely building any units. You are going to get hit hard and you should be preparing for that inevitability. It may be possible that either one of them may bribe in other AIs as well.
5) Ultimately goal is to always be running 100% research. If you can't then you should either get the gold to do so, or run tax to get it. At this stage with the all the beaker modifiers in place, you can run just enough of the slider this turn to have enough to run 100% next turn to finish Banking. OR just trade something for the gold to finish it now. OR just trade for Banking..ha. Trade stuff, man!
There are probably other things to point out here, but it is important to emphasize here that a lot of your mistakes were made very early. IV is very much about do things right early so they snowball later. If you really want to learn to play at this level, I'd recommend playing games here from the very start. Anyway, as for this game I would look to try to improve you diplo situation as best you can as soon as you can based on some of the things I mentioned earlier.try to get an ally. If you can bribe someone on someone that might help that might help. Start building your best units available now - everywhere - as you work toward Rifles. You probably want generous stacks on both Russian and Celtic borders cause the jokers are comin' at ya. It's a tough road it appears but may be manageable...I'd have to take a deeper look.
on another note: