PEP is very effective. I hate to give you a number here because there is nothing called 100% in medical science. However, a very large population wouldn't test positive after successfully completing the regimen for 28 days.
You started it at a good time. Not every one around us is HIV positive, you are only guessing that your partner was positive. Also, if he indeed was positive, if his viral load could be most likely low being on ART that apparently implies less possibility of infection.
The best thing to do would be is to reach out to this person and ask direct questions, most people would not lie. However, I understand that's easier said than done, if you did have access you wouldn't have been here, maybe!
Therefore, some do's and don'ts for you to make this easier, do not miss your dose, if by any chance you do miss a dose, it is better to take the pills a bit late rather than not at all. Check with your doctor, but don’t double your next dose. Keep away from symptom surfing they don't mean a thing. Never did. It never will.
After you finish your PEP you need to wait for 28 days to get a IV Gen HIV test, at that point, it will be able to provide you with an indicative result, infact that result changing ahead will be unlikely. Test again at 6 weeks for a conclusive with the same test mentioned above and get over this.
Keep following up with your doctor for information on PEP and testing guidelines and options.
I think you are going to be okay this time. Just a word of advice, you don't dodge a bullet every time, insist on condoms next time and use it correctly to stay away from HIV.
We wish you good luck.