BF blowing up because he thinks child isn't his.

So my boyfriend of 8 years and I have one child together. A 3 year old little boy. Our birth control failed with him. I just switched from the pill to the ring and the ONE TIME he decided not to pull out, I got pregnant but was still using a different from of birth control. Well now after 3 years, I got on the IUD. He also still pulls out and has every single time. Well I was feeling very ill and went to the doctor and they said I was PREGNANT! I do not know how cause they IUD is in and we pull out. So now he thinks there's no way the baby is his!! I did not cheat!! Never had, never would. I know it does seem weird to get pregnant taking all those precautions. But isn't it wrong for him to even think that?!!