Should I be upset?

[user1480775842]

My fiancé is just getting back into contact with his 4 year old son. He communicates through the mothers parents as he will not talk directly to the mother.
The mother is not allowing myself or our child to meet this child but all of my fiancés family are being allowed and are going up one after another.
Last time they were in contact the mother said we should all meet so the child could meet me, every time we organised it 3 times in all she cancelled and then decided she didn't want me to meet him at all.
This brakes my heart because my fiancé now has a seperate life away from me and our son.
I want to be a part of this with him support him and be there with him as a family and this woman is not letting me meet him!
My fiancé is also getting very angry at me because I want to be involved?

So originally when he started paying he was paying very little a month because there was no proof the child was his and it was between two men, she cancelled every DNA test that was arranged (I don't see how she can do that!) eventually last year we payed for one privately to get it confirmed.
This has been tried so many times but everytime she ends up saying no you are having nothing to do with him anymore. Then a few months later or so she calls and my fiancé goes running.
BUT I am not surprised he has another son that he wasn't allowed to see!
If this woman was sane then I don't think I would mind so much but it's just how insane she is and how many times she has messed with our relationship now.

The mother in INSANE I feel sorry for everyone who has to deal with this woman. She has no told her family they are not allowed to communicate with my fiancé on Facebook at all anymore!
Honestly it makes our relationship so hard and we argue a lot because of it... but I think he is just hoping it will get easier with him and we can take him and do our own thing with him. I don't see her letting us do that for a very long time.