[Luuuuuuuucy]

We've been together for a year and half and been living together for almost a year. I met him 2 years ago while he was separating from his ex. We first became great friends before we got together and I also helped him to get through the hard times after their separation.
He's got two lovely 26 months old twin boys with his ex who were introduced to more then a year ago. Since then we've been hanging together 2 or 3 times a week and got close.
My partner and his ex rarely did things together with the kids as they didn't get on well.
But lately she started initiating activities for them to do together.
I'd love my partner to spend as much time as he wants with his kids as he loves them and they love him to but I feel left out as I got attached to them to and I consider them as my "family" and it hurts when they do things together without me.
His ex doesn't want to meet me. We bumped into each other couple of times and she was always very polite to me. But at the same time she doesn't want me to be even waiting in the car while my partner picks up the kids.
I also recently saw a phone message from her saying something about them going together to Disneyland and my partner replied that it would be awesome.
My partner gets easily stressed so it's hard for me to talk with him about these things. He always says that his ex would go crazy if he did this or didn't do that. Which I had respect for at the start because of the children involved to but I'm now losing it.
I should probably also mention that I had an abortion when I got pregnant after we had been together for 9 months because it wasn't "the right time" and I'm still heartbroken.
My partner is a great guy and we recently went overseas together to meet my family.
But I can't get rid of this feeling that there's something wrong.