I was kinda expecting some kind of explanation as to why he even went to stay with Grace.
Because his parents are away for 3 months and he hasn't learned how to look after himself so he's gone to stay with his Aunt. That's the explanation the game gives right at the start.
He could have just stayed with his hot GF and got a normal job for a few months instead of leaving his hot GF behind and working at some failing bar probably lucky to be getting paid min. wage with no tips.
The GF has gone back to stay with her parents for the summer, so it might be a bit of an awkward imposition to ask that her BF be allowed to stay with her in her parents home for 3 months.
As far as I can see either MC is going to be cheating on his GF or the dev is going to have the GF cheat/break-up while MC is away thus freeing up the MC's relationship status, neither of which seem very appealing to me.
The MC and Mia will get back together, I think that much is clear. It may be possible that they will rekindle their sexual relationship but it acts as closure for both of them and allows them to move on, but this would likely be a choice with the other choice being to stay with Mia in a loving relationship.
But mainly after the way the first SWM ended [and the apparent complete lack of contact in the following 2 years] I don't know why the MC had any interest in going to staying in the same place.
Well, for one thing, it's for plot reasons, but also, why wouldn't he want to see Mia? I'm sure he wants to patch things up and this is the perfect opportunity.
Maybe I'm just weird, but I've never been one to chase after a girl who's started playing 'games' or has made it clear she's not serious about, or not interested in, staying with you.
But she's not "playing games". She started to fall in love with him and right when that happened, she found out that he was fucking their Mom and it made her feel that he didn't reciprocate her feelings or care about her as much as she thought. So she left to get away from him to start a new life and try to put the past behind her, but she clearly hasn't got over those feelings.
So really what this is is the story of jilted, unrequited love and she's definitely serious about him and does want him, but she doesn't think he feels the same about her, which is why she left and why he needs to realise this is why she left so that it can make him see that, deep down, he feels the same.
Right, but if the MC has matured then why is he leaving his current long-term GF behind for 3 months?
Because we all know that either he's going to cheat on her or she on him in order to enable the MC to start hooking up with either Mia or the new characters, right?
It would have made a bit more sense if the MC wasn't currently involved with anyone else.
Yes, he's going to cheat on his GF, but that's not a lack of maturity, it's because Mia is the love of his life and he'll finally wake up to that fact. By giving them both relationships, it raises the stakes of this taboo relationship and adds more interesting drama to the proceedings because they have something to lose, and it becomes a moral dilemma of whether they try to move past these feelings, or embrace them and disregard how society views such a relationship in favour of their own happiness.