Yes, by all means, leave the girl you are currently with for the younger, sexier one.
Your current girlfriend treats you very well, is ambitious and loyal to you. But who wants all of that stuff when you can have a hotter, younger indecisive girlfriend?
Do your current girlfriend a favor and leave her now so she can find a man that will treat her well, as she deserves.
The answer is simple!
Are you in love with the one who treats you like a king? If not, and she is in love with you, then she will probably be happy to have you are even if you are not in love with her; which really is not fair to her.
If you are not in love with her, do her a favour and leave her so she can find someone who will treat her like a queen. You do not deserve her and I say that with respect because if you are not in love with her, that is not your fault. She however deserves better than you!
I am presuming that you were never in love with her because if you were and you fell out of love because of the younger woman, I am tempted to say that you are a jerk.
But at the same time, things happen that we have no control over, so regardless, you still need to leave your woman so she can find true happiness.
As for the younger woman, well it is up to her…..you have nothing to lose though except the bird in the hand, while you chase the one in the bush!
BTW, why do you say the 2nd one is “marriage material”? From your description of how she treats you, it doesn’t sound like it.