I had sex with my ex on february 19 & someone else on the february 23. test says my date of conception is february 23 which is most likely to be childs father?

It takes a few days for sperm to reach the egg & conception to occur. Early dates are often inconclusive. The only worthwhile answer & one that will hold up in court proceedings will be a DNA based paternity test. The NIPP is a non-invasive test performed on your blood as early as 8 weeks. They find fetal DNA in your blood & can test it for a variety of things including paternity. Could be either.