Hiding things

Hey guys

I kinda need your help, I don’t know what to do

My bf and I were talking about his car and my dad (he wanted to help him with the car anyway) and at one point my bf says ‘but don’t tell him that X’ and I say ‘well I’m not going to lie to my dad, not saying something with a thought behind it is lying’ and my boyfriend says ‘no it isn’t lying’ and I’m like ‘oh well then have you done that to me, hiding things so that I don’t get mad or something?’ (Thinking he’d say no) and he says ‘yeah oh course!’

We’ve been together for three years and we’ve already had a conversation about trust a long time ago, we agreed we wouldn’t lie to each other or hide stuff but now it’s like he’s completely changed and thinks hiding things is normal!

I don’t know what to do, please help me, I feel so betrayed

EDIT: the problem isn’t my bf not wanting to tell my dad, the problem is my bf said it was normal to hide some things from me so I don’t get mad

(And I obviously know we don’t tell people our stuff, this was an exception bc my dad needed to know in order to help him with his car)