nope, dont do it....like others have said: if she wanted to leave him, she wouldve done it already...dont make excuses like 'he knows how to take advantage of her weaknesses'....if she is as keep-able as you say, that means she wouldnt have to worry about being single for long, no matter self esteem issues or not...she aint left cause she dont want to....she enjoys your company and the attention you give her, and you seem to enjoy hers, but leave it at that...dont try to take it further, you only setting yourself to get hurt...hell, it might be best you leave her alone for awhile, cause you've already started setting yourself up, thinking about being with her as a couple.....