idk what to do

I feel hurt and lefted out My s.o. and I have been together 4 years His children's mother lives with his parents We went out shopping Saturday and he drops me back off at home before going to his parents house I feel like I should of been able to go like she know who I am and everything so why couldn't I go and I think he got her a card which he could of just told me its like he was being secretive but my feeling are Hurt cause I didn't get to go shouldn't matter about her being there I didn't tell him good I feel should I just let it go