The issue you have here is that you had sex with both your husband and the EX all very close together. I understand you used this VCF, however there is always a chance that not all sperm were killed as sperm can live for days in a womans body, this is why some women can get pregnant with sperm that is 4 days old in her body. Also the ovulation day can vary every month as well. Your best and safest best to determine who is the father will be by doing a DNA test. You could hazzard a guess at who the father is when you get give your due date, but i think you should just wait until the baby is born and do the DNA test. Hopefully the child turns out to be your husbands.
I agree, your going to have to wait to find out once baby is born. But relax and don't stress (easier said then done, I know)...your having a baby and that is wonderful! I am sure everything will work out in the end. To a healthy pregnancy and baby!