This is my first post on this board because our situation is so oddly similar (minus the kids on my end and I'm 32, hubby is 36, gf is 26) that I thought maybe I wrote this posting in my sleep or something! Seriously, same exact situation - including a VERY Italian family on my side. We've been married for 5, together for 9 with our girlfriend for 8 months. Hubby met her, starting dating her first - then I met her. We hit off and all dated, eventually into a committed relationship. So maybe I can offer some insights - since I know how you feel!
Firstly - I view our triad as 4 interconnected relationships (me-hubby, me-GF, hubby-GF and the 3 of us together). For me in order for the triad to flourish, all of the relationships need "watering" (love & attention). For me, it's important that hubby & gf have quality time / develop their relationship, just like I try to go on date nights with just her so we can get to the same level / talking about meaningful subjects / deepening our relationship (which in the beginning wasn't the case - I felt similar to you but now we've broken past it).
Secondly, your feelings are totally "normal" (whatever that means!
) I felt similar. Give it time. Think about their perspectives and try to understand the "why" behind things. I find comfort in that and it helps control my negative emotions.
Also, I asked a lot of questions about how she feels on various situations/topics so I can understand how she thinks/ her POV. I realized that in beginning she was most concerned about how I felt, what I thought (about her), she was often nervous about her actions and how I'd take it. I realized that she's in a very vulnerable position, so I needed to make her feel as welcomed and comfortable as possible - which could mean more time with hubby/GF and less with me for both of them. (This is true even after 6 months together). Things take time.
Let's talk more - because I bet we have lots in common!