I thought of something else, as far as the "spending money and time" bit. This was brought up over Thanksgiving, during which our host expressed desire to move forward in life with other people interdependently, instead of alone/independently. I did not express my opinion at that time, but I will express it now - and it may or may not be relevant to your situation:
I can enjoy creating something out of nothing WITH other people - I have no aversion to combining efforts to build a life together. But when it comes to jeopardizing what I already have - I will not put that at risk where other people can contribute to possible loss or failure over which I have no control.
For example - I would share my home with a friend who needs a place to stay, but I would not sell my house and put the money into buying a piece of property with other people.
I'm thinking that when your husband met you, you both had "nothing" and built a life together. Maybe now he "feels" the same thing about this girl-friend, but you and he are in a different place in life now. You won't "recapture youth" by trying to repeat the experience with someone else, and you might even lose what you have if you risk too much too soon in trying to achieve that.
Also, the girl-friend not wanting to talk about shit is not very encouraging. I don't care who or what you are, but sometimes you HAVE to do things you're uncomfortable with in order to put things in order and move forward (see the thread I started about "Comfort Zone" for more on this). Other people cannot do the communicating FOR you just because you don't LIKE it.
And yeah you are very right when you say there is a difference between holding hands / being affectionate and being "in a relationship".
I'm not sure if there is anything you can SAY to your husband that will get through to him. But there are things you can DO (or NOT do) that will SHOW him you are serious.
What if you just tell him - "Go ahead and spend your OWN money and your OWN free time getting to know her. I'm not in a place where I can do that with mine."
In writing this post, I have come to notice that the more you resist, the more he will try to push for it. Just let him go do it - but don't offer to risk your own self if it is not what you want deep down (it doesn't even seem like it is "deep down" with you - you seem to know very well what your parameters are). Let him learn for himself whether or not she is "relationship material". You may be pleasantly surprised - but these things don't happen overnight. I'm not sure how old you are, but I have discovered that the older I get, the more quickly time seems to pass, and the easier it is to wait for something. When you're in your teens and 20's, you want it NOW NOW NOW, you don't want to wait another year OMG! But as you get into your 30's and beyond, a year or two is really not that long at all when it comes to getting to know someone - especially if you're entertaining the possibility of having the person in your life for the long-term.