Feel inferior

I feel inferior to my boyfriends ex!
They have a child together so yes they need to have contact but it bothers me that he feels the need to hide things about us all the time!
First it was our relationship, then that we had a holiday booked and now because we have moved in together.
I feel hurt by him not saying the truth when she asks....is that silly of me???
I want to feel like I'm better than her & that our relationship is serious and going in a good direction but by him not saying anything makes me feel like he doesn't want her to know.
He scared she will not like it and say he can't see his daughter or she won't pick her up...she lives 100miles away and he picks her up & she does when it's time for her to leave.
He thinks she will ask for more more coz we live together, he pays her more that what he should and doesn't begrudge it 1 but but its like she scared to upset her which upsets me.
Am I reading to much into this or am I justified in feeling the way I do????