Listener question: I've been lied to

Not that long ago, I found out that someone who means a lot to me has been deceiving me for months, hiding the truth from me and essentially lying even though we had conversations about that and promised to be radically honest with each other! It hit me like a tonne of bricks. That truth, had I known it, would have changed almost everything in my relation to this connection, my decisions etc. All of the sudden, since I found out, there was very much the separate me who was hurting and felt betrayed by this person, the separate other. I noticed that this has always been a huge thing for me. To know the truth and the thought of someone who I deeply care about hiding something from me (for mostly selfish reasons) that has to do with me and /or directly affects me brings a huge amount of anxiety after the fact, caused by the utter disbelief that that person I trusted fully could have done this to me. But it’s always only after the fact, when I think back to what happened. There is not distrust or anxiety when I enter any relationship, interestingly. I ask myself, what’s at stake here. Why when I find out someone I care about has been deceiving, the utter disbelief that they would do that TO ME and the anxiety that comes with that and then the self-blame for not seeing that are astounding! It doesn’t even help knowing that in a way I’m a hypocrite, because I have hidden the truth from people I care about, I simply thought my reasons were noble! (Laughing at myself as I write this part).  The impact of it really caught me of guard as I never thought that something like this could hit me this hard anymore. I know that this is a personal story but I feel that I’m not the only one who’s been deceived or lied to by people who we care about so I thought others may benefit from you addressing this subject. I’d greatly appreciate that.