The Nicole relationship (or what it is at this point, more of an open if we consider the FFM scene) is clearly one of the most honest lines in the game. But in a long term it would not really work out well in my oppinion.
1. she has a kid, an unknown bagage as it has said hereearlier
2. a really big age gap putting off the balance of the male-female roles of the relationship, pushing things on Nicole's side more into a mother role with MC too regarding she is one ATM and the third point, which is.
3. MC clearly has issues not having a female role model in his life as he grown up and not having a mother could form his connection to women (and I think it's forming in the game)
IMHO the best pairing with the MC therefore a bit older more confident woman, but with less age difference than Nicole. Bella maybeon the edge of this, but she has her own issues...
I think Sage is still a good candidate, even if she has issues, or had in the prev. chapters. Breakups are no walksin the park, even if you had enough from the other half... we do not know how long they have been together, what they past is exactly, how they relationship worked at the start, we only see a glimpse where Sage suspects Chad cheating and when she gets sure enough, goes for revenge. Sage said she do not like to loose, and she is fierece, confident and somewhat wrathful too. She is not used to being cheated on, nor being thrown out.
It is not a good sheet for her to start with MC as a tool of revenge, but in the game things quickly start to move somewhere better, discovering a more healthy dynamic with MC for herself. All in all, I won't blame her about the Chad issue, it takes time to move on and after every break up the scars of the relationship remains for a longer duration. I think she will face and learn from this experiences as well and allwhat happened could form her a sutiable partner for the MC.