When the tough love technique does draw them back, is it because they really want back in on their own accord?

My guess is no, it's more likely they came back because you cornered them, out played them in the chess game, so to speak.

Is this the best way to build a truly loving and lasting relationship?

After the Last Chance Technique indeed.

M: A really long time.
Crisis: 5 years.
She's still worth it.

Life is never made unbearable by circumstances, but only by lack of meaning and purpose. -Viktor Frankl