I only took the first pill for abortion. is it safe to have sex before taking the other abortion pill?

Really! NO!: Why don't you solve one unintended pregnancy problem before you create another. Once the 2nd pill is taken the cervix (mouth of womb) will open to allow the pregnancy tissue to pass, but it will also allow bacteria from sexual encounters to enter and infect the interior of the uterus. I hope that the ensuing cramping and bleeding will make having sex a very low priority.