@Zbax,
I would imagine that he has known her a long time.
In his 30's not married, but gained a female "friend" to go out with, hang out with, do things with instead of being on his own, all the time, which is hard at any age. This is normal until someone special comes along, less time is then spent BUT, you don't ditch good friendships, they remain.
I would also imagine that his family naturally know her quite well, so why wouldn't she be included.
3 Months and you should both be giddy still. But it doesn't mean you are included in family events, 12 weeks you don't know each other that well yet, just getting to know each other. You meet family when it appears things are going places.
You are a "girlfriend" and new at that.
She is a "friend" who has been around a long time.
Quit with the jealousy as it will certainly cause a break up, as you will make him choose.
Chill as well, 12 weeks remember not 12 months.
Lastly, he needs to learn to clean himself neither of you are his Mother