In case you forgot... Jessica was not on vacation. What happened to her, changes people, and it does a lot more than that.
I'll give you the answer I've given over my discord a few times, already
Jessica has been through hell, and she doesn't want to share that hell with him, so she has closed herself off, and is trying to suppress her feelings. She feels like she is not worth his love right now, so she is focusing on being a mom to her daughter.
It is now our job, with the help of our other mini-harem girls of yours to help her open up again and hopefully, she'll stop feeling that way. And maybe later we can make everyone involved pay. Perhaps after that, she will be able to move on.
For the time being, we need to show her that we only care about the present and show her that despite how "unworthy" of our love she feels, she doesn't get to make that choice, for us. We still intend to love her.
We will get that chance with this coming update.
Melissa is initially shocked, as would any sane person when met with such an insane bomb dropped on them, but in the end, she decides that it is better than the alternative which is only implied, but that is the point. This isn't Harem "let's fuck everything and they all love us instantly mode" They have personalities, and they make choices, decisions, and even act/react to things, based on those. Melissa obviously wanted the MC to herself from the start. Alison fell in love with the MC almost immediately, seeing as he was her saviour and her guardian. Alice fell in love with him because of how nice he was to Alison, and herself on many occasions.
However, with Jessica back in the picture... They were conflicted, unsure and based on choice. Even willing to let go, for the sake of that kid.
As for the rest, Jessica is herself only when we choose.
Alice/Alison before going to rescue them. If we choose Melissa, Alice does not feel the same sense of urgency as one would when rushing to save a loved one, and perhaps there is even a little jealousy in our ever learning AI girl. Like it or not, that's the character. Which brings me to the two different Jessica outcomes.
You must have missed, or perhaps forgot that one of them is being controlled by Alice, for Maria's sake (When Jessica doesn't make it). When we choose Alice/Alison - Alice rushes there and makes the shot before Jessica gets shot. Which gives us the real Jessica, being alive as a bonus/consequence. Later on, you are once again given a clean slate to choose a path. Cement the previous choice, or change it to another. With this coming update, we will end up with no less than 3 dif endings, plus a prego/no-prego version. So, a lot of work, and this one will def take a lot longer.
Anyway. The answer will be included with the coming update, for those who do not wish to spoil it now and wait a month or 2 for it, lol. Take care, I'm going back to work, and will likely go silent for a long time, once more.