You seem to have all the answers' young man & are looking for someone to ratify them.
Yes it does appear that to begin with, the TPHA report was false positive.
It all depends where you did it, what technique used, why no titre?
It is possible to get a VDRL
negative & a TPHA positive as an authentic result.
Your doctor probably knows best but i do believe the 100mg once/day dose is half a dose & in your particular scenario, need have been continued for either 2 weeks or 28 days assuming the thought process was linked to treatment of secondary/tertiary syphilis
is less likely to end up with similar results as opposed to penetrative sex.
However, in genereal, it is best to practice SAFE SEX
irrespective of your sexual leanings & preferences!!
Stay safe & trust this answers' all your queriews'..Good Luck!
Dr Praveen Rodrigues MD