1-Hassan lost his purpose . The SYSTEM no longer needed him so he no longer was forced to play the goofy comedy relief character anymore. He lost his only role.
Much like us ''real humans'' when we lack a purpose in life we become self conscious , anxious and look for ways to escape reality.
2-You can thank him yourself , he commented below under the username ''Tekkentag''.
If it weren't for him the series would have definitely remained in hiatus.
3- Nessrine's fate is actually addressed in ''Milker 2'' ( which is still in development) . There are some hints about her in few games in the series especially Milker 1 but anyway her fate is not related to the events of Happiness 2 because her route in that game is not the ''True route''