Hello, i am making this thread because i came across many people who complain about Sitri and how he screws people over and doesnt deliver or stay in contact much. (like a guy with too needy girlfriend :D)
To start i want to say, Sitri is a pretty powerful and extremely dangerous demon (in case you want to trick or betray him, or not keep the bargain). He wants summoners to be interesting enough for him, and if not he sometimes casually just drops deals (pretty ironic, since he despises the summoner to try something similar)
In my personal experiences i had awesome results throughtout the years, but Sitri demanded me to take several of his points of view. (which he revealed gradually, when he saw i was Ëťall inËť, implementing everything into practical reality, and changing my lifestyle by force). He wants people mostly to be really honest and make deeply personal and long term deals. He also makes short term deals, but mostly with people who are quick action takers and dont want any fluffy lovey dovey shit, and if they are naturally open in perspectives about sexuality, and see it as fun, not something serious. You can also use him to make people lust over you and want to do all kinds of perverse things (but the chance of that coming through depends on how amusing he will find the encounter if he makes it happen). Basically he wants sex to be in his taste enough for him to enjoy it as he is also experiencing it through you or the other person. 
Now to connect to him, you might want to first meditate on some of his viewpoints.
He doesnt believe Love is something special, but believes in nature as in natural forces. He finds people who shame and judge any forms of pleasure and intimacy, to be absurd. He holds a uniqule neutral perspective which allows him to get everyones secrets (because of his neutral position) He holds number 12 as he said it represents god in some way. (dont know why that is a thing with him to be honest
He worships beauty and intimacy, as he says it creates more uniquely enjoyable vibrations/emotions. He dislikes ugliness.
Now to the sexuality, he doesnt accept people trying to manipulate others, but instead encourages shameless acceptance of ones nature and he mocks those who have shame in their hearths (he sees it as the lowest possible vibration, and most unnatural thing one could feel). He doesnt see a point in seeking meaning in things, but accepts all views and laughs at the seriousness of them.
He doesnt like domination (except in a sexual way, if one side wants to fully play dominant and other wants to play as slave). He also sees force as weakness, and thinks it is only weak beings that need to force things in reality. He instead plays with it like a child plays with toys. (self amusement, joy and glorification of infinite forms of beauty and potentian fun experiences in creation)
This is from my pretty personal and long term working with the demon, and it is part of the deal for me to share this information.
Now this will be all i felt obliged to share at the moment, and hope some people being drawn to this mysterious demon will be able to keep him amused and have some fun together 