Also, if you are having sex with a previous partner who has not been treated, you could indeed be reinfected.
Why hasn't your previous partner been treated? You should let your partner know they need testing and treatment, and not have sex with that person until they have done both. They could be spreading it to others, and untreated infections could have serious long-term consequences for them.
If you are responsible enough to have sex, you should be responsible enough to inform partners of these things.
Well, condoms should effectively prevent mycoplasma, however sex is never precise, there is secretions etc etc etc, moreover condoms sometimes break, slip off, so the prudent and the right thing to do is to abstain from sex untill cured, not to mention that you put yourself at risk for other stds, as raging mycoplasma infection makes the tissue more succeptible to other patohens,and sex is not something vital for sustaining your life. Why have a burden on your consciousness if you transmited or not, just abstain untill cured, and after that condoms.