I have been with my partner for around 18 months. We have lived together for around 3 of these. All is absolutely fine in the relationship apart from one huge issue which I am struggling to navigate. I have 3 DCs in their late teens who live with me full time. They see their dad but due to their ages, prefer to have one base. He has a 10 year old son who he sees mainly at his ex's house (they split up around 8 years ago). The time and days that he sees him varies but it is around 3 or 4 times a week for several hours. This in itself is a little challenging in that he seems to play house there iyswim. However, I do suck that up rather as the arrangement pre-exisits our relationship, I want to be considerate of his son's needs etc etc. In addition, he hasn't told his ex or son that he has a partner. They are totally unaware. Every time I try to talk to him about this, he just won't discuss it so I have no idea what the reasons are.
I am torn between bringing it up again, and staying quiet, swallowing my feelings and leaving things be for the sake of harmony. I feel like the other woman. He is entirely in my life and yet I am only in half of his. I am quite prepared to be told I am being completely unreasonable and I should just let things lie. I suppose I would like some perspective on whether it is something I should accept and wait until he decides the time is right to tell them or whether this is potentially relationship ending.