So when did your partner test positive for syphilis? Did he say what kind of treatment he'd gotten?
Your chances of syphilis are low if he had no visible sores, but I absolutely understand the concern. Typically, when someone has a positive TPPA and a negative RPR, it does mean that they were successfully treated for syphilis in the past, and it's no longer an active infection. It could also mean a latent stage infection.
The best you can do is keep testing. A syphilis test is conclusive at 90 days, though most will test positive by 6 weeks.
The red spot you had - a syphilis sore will be a round, painless sore. If you google a syphilis chancre, you'll get a good idea what it looks like.
So test again in another month or so, and that should be good.