That really depends on how you interpreted the ending of the first game. Was the MC really in love with Mia or not? How much did Mia leaving impact him? If he loved her it would make sense for him to break up with the mom and start 'growing up' so to speak. He clearly matured a lot during those two years, and I don't think the mom breaking up their relationship would warrant such a big change in character. So, in my opinion the MC loved Mia, he just realized it too late. The taboo nature of their relationship meant that neither of them took each other seriously. Both of them loved the sex, but neither of them showed that they would want something more. I think the whole making incest porn plus having sex on stage drove a little bit of wedge between them, at least from the MC's perspective since he wasn't really keen on those ideas. If I remember correctly that was around the time he started having sex with the mom. The mom at that point represented something new and normal (meaning not fucking on camera etc.) so the MC was more keen on her. Mia then started catching feelings and acted weird because of that, while the MC had to deal with the whole blackmail thing which again drove them further apart a bit. At the end the MC realized he fucked up and was ready to talk about his feelings, but Mia shut him down twice. That for me proved that he definitely loved her at least in his own immature way. Now for this game the choice is there, so I guess you can also go with the other option in which case there was no love, but honestly I just can't see that ever being an option.
As for what the choice means in this game? I think it's pretty clear that the game will be about proving to Mia that you love(d) her and that you changed, so what better way to start doing that by saying that you broke up with the mom even though you didn't really have to since Mia wasn't in the picture anymore? Regardless of the answer the MC clearly states in his thoughts that he is going to tell the truth so he is definitely not lying.
