I have a 6 year old niece, my brother's daughter. His ex got pregnant very early on in the relationship, so I have know his ex for about 7 years. We became very good friends, best friends basically. My brother was an arsehole a lot of the time and they eventually broke up for good about 3 years ago. My friendship with her continued until there was an incident that caused us to fall out about 2 years ago. However, we stayed civil because my relationship with my niece is important to me and facilitated through ex-SIL as my brother only has contact once a week.
I've been helping ex-SIL out a lot over the summer with childcare, which I offered to do because I have a lot of flexibility with work and know ex-SIL struggles to find childcare because of her shifts. Our friendship has naturally grown and we are having days out together with the kids etc.
Now the issue is that my brothers new girlfriend has recently found out she is pregnant. She is also seeing my friendship with ex-SIL develop and confided in my brother that she is upset about it because it feels like I've chosen his ex over her.
As far as I'm concerned there's nothing to choose between. I'm not close with my brother (I'm a single mum with very little support from my ex, so I absolutely judge my brother for his lack of involvement in my niece's upbringing). I have met his current girlfriend a number of times and think she is lovely. I have been kind and welcoming to her. I just don't see them often because my relationship with my brother has deteriorated.
I don't really know what to do. Again its a relatively new relationship and in all honesty I gave up on befriending my brothers girlfriends a few years ago because he always fucked them about and then I would lose a friend. So I am a bit more distant I suppose. Also she is early stages of pregnancy so perhaps I should be a bit more sensitive to her feelings. But I don't know her well enough to spend time with her without my brother and I don't particularly want to spend any time with my brother. Am I wrong to start rebuilding my friendship with ex-SIL at a time when it is is a bit insensitive to my brothers girlfriend?
Or am I massively overthinking this?!