Hey everyone, I need advice.

So I was on the Mirena IUD for 7 and a half years, recently got it removed in May. I’ve been with my current partner 2 and a half years, and have discussed the possibility of more kids, but in the future. He has 2 kids from a previous relationship that we have pretty much full time. We talked about whenever I took out my birth control around October (the expiration for my BC) we would start trying. However, i was experiencing pretty rough symptoms with my IUD so I decided to get it out early without telling him, kind of a last minute decision. My gyno assured me that it would take months for my cycle to regulate, especially since I’d been on BC for so long, that I shouldn’t worry too much about getting pregnant, and we weren’t having regular intercourse anyway, so I wasn’t worried. But a few weeks ago, I found out I’m pregnant. I’ve already told him about the pregnancy, but he’s under the assumption that I still had my IUD, and because I was stressed and overwhelmed with the pregnancy, I let him believe that. I’m worried that if I tell him, he’ll accuse me of trying to trap him (which is untrue, we’re already engaged and are planning our wedding) or that he’ll be so upset with me that he’ll want to break up. He also suffers pretty severe PTSD from his last relationship with the mother of my two other kiddos so I’m already preparing for the worst. My first ultrasound is coming up in a few weeks, and if he goes, I’m worried it’ll come up. What do I do? Obviously I know I need to tell him the truth but I’m just not sure how to approach it while trying to not stress the baby, since I already don’t handle stress well as is.