How should I even feel?

In March my boyfriend left me to be with someone else. I knew he was dating her and I will admit I was wrong and I was still going back and sleeping with him. After only being with her for 2 weeks he decided maybe it’s me he still wanted and I gave him another shot. We’ve been dating since then without a single problem. Last month I found out I am pregnant. We already have one child together so we’re stoked for another. We decided to move back in with each other and looked at a ton of places today. One I fell in love with. He seemed excited until we looked at the bigger style of the apartment in that complex. Soon we get in the car and he said, “I want to be honest with you so I’m telling you now that’s where she lived” he always told me before he never went to her place. So I’m hurt and upset knowing he lied about being there. I also now feel even more disgusted with myself because I allowed him to sleep with me while sleeping with her. Should I even feel this upset and hurt when I was the stupid one all along?