As for Ren'Py, you can download the latest build and read through the demo game (The question should have its script unobfuscated, so you can take a peek and learn from it). Yes, Ren'Py can make dating sim games, you have to use the DSE (Dating Sim Engine) to do so; it's a separate download, you can look around for it on the Ren'Py site.
Mugenjohncel recently also created DSE the game, which is essentially a game demonstrating how to use Ren'Py's dating sim engine's functions, as I understand it. When you say you want to figure out how to make the relationships between characters work do you just mean you want to figure out what sort of code to use?
This tutorial deals with exactly what it is titled as... Also it goes into stuff about a sequenced dialogue path.
It is assumed that you have general knowledge on flash (I USE MACROMEDIA FLASH PROFESSIONAL 8).
Lots of players get turned onto these aspects from story and character-driven Bio Ware games like Dragon Age, and if you’re a fan of those, I have a few recommendations to help welcome you into the otome genre.
While all you need to be “good at” is reading and making choices -- don’t worry if you don’t normally play games -- there are some important things to know about how these games work.
Welcome to Otome, visual dating games made with women in mind.
These games are often designed to be played multiple times.
I then unzipped the contents of the DSE inside my Projects directory.
Then I got back to the main Launcher page and chose "Select Project" - the DSE is already there.
Of course, creating any kind of game is such a broad topic that it's going to be very hard to "teach you" in a forum post, but hanging around the places I listed above, lurking a bit and peeking inside other people's code (when they leave it unobfuscated for that purpose) should, over time, allow you to get a good understanding of what to do. Haha~ I find it hard to make a dating sim game with it. Just worry about how to make it into a dating sim game like make the relationship between you and the guy or girl closer. I'm afraid that for that you'll have to dig around for tutorials on the DSE (Dating Sim Engine), as my field of knowledge is more on drawings than coding.
Which part of my post do you find particularly hard to understand? After running Renpy's launcher I chose "Options" from there and created a Projects Directory.