I have good news for you. You don't need to reroll your character to romance Mako; you're on the right track.
So, like I stated in that Torian the Terminator thread, I'm not even at Taris or even Dromund Kas' second visit a la Act 2 on my Powertech and am sitting on 9060 affection with Mako, not knowing that having more affection with her than Torian (who I don't even have yet) could lock me out of the romance. Now, she grew on me as a character and all and I do not see myself liking Torian in the slightest and since we simply can't kill unwanted companions off for good, I must ask, am I screwed?
If not, then do I just level my Underworld Trading alt up enough to then stuff Torian's face with Rank 6 Companion Gifts, or do I just reroll my whole character? Of course, after reading how Mercs with Concussive Missile have it way easier than Powertechs against those two guards, the idea to reroll in already in my mind.
The circumstance you were told about doesn't happen based on having certain levels of affection with one companion or another. It only happens if you are not yet in a romance and even then, you have the ultimate choice over encouraging the situation or saying "no, mine!"
Hope that takes a load off your mind.