Trust. Faith. Love. How do you know when you start? How do you know 10 yrs in, 15yrs, 20, 30. I know my level of commitment. How do I know theirs?
You know when you start when you're strong enough within yourself. When no one can make you dance to their tune by pushing your buttons, because you haven't got any. When you're so sure of who you are, what you stand for, that you are indeed loveable, valuable for yourself, and YOU love and honor yourself.
Once you get to this point, you will not look for someone to fill the holes in your life or repair your wounds, nor will someone that is looking for just that be acceptable to you as a life partner.
That's why the work you're doing on you now is so important. That's why even if she chose to come back , you might not take her back because you've grown in emotional maturity and compassion. You will realise you can't take away her pain, fix or heal the wounds to her self-concept/esteem. You may choose to be friends, but never at the same level of intimacy you once shared, unless she CHOOSES to grow too.
As to their level of commitment, you can't really know it, but you'll have clues.
The surest clue is their family history. Listen to it. Really listen. Where before you heard their life story and you thought, " Oh, I see, well they're a good person, they've survived a lousy family history/abuse/addiction etc.etc. and they're ok!" This time you will think, " Whoa! There is some significant wounding here, a discernable pattern, and they are badly hurt." You will also see it in their behaviour because they will have buttons that make them behave childishly, self destructively, and over the top.
What can I tell you 2Step? I'm still learning, but I'm seeing this more and more clearly as the weeks go by. I hope my sharing has helped your understanding.
BITS Me-51, WAS-52 Kids 2 M-26yrs, H.left 2009, 2 more Bomb drops, Reconnection spring 2013 Change is inevitable, personal growth is a choice. Love is a action and choice you make, every day.