Your description of your husband/"other" experience is familiar, as are some of the elements of personality, with an important difference: Investment.
It took ten years for our/his stuff to come to a complete head (we are 14 in now) of lies, betrayals and severe acting out, although in retrospect I should have seen it all coming. We are still picking up the pieces.
Joint therapy did help quite a bit, especially with the immediate issue of his ability to stop justifying his betrayal with complaints about me.
This book: After the Affair/Janis Abraham Spring, PhD, was also very helpful. It is written for both parties, the betrayed and the unfaithful (I though it would tell me to get over myself, but it was actually very affirming and helpful). It is a good idea to get your husband to read it, too.
I can't say whether or not I would make further investment in your shoes, knowing what I know now. It is a sacrifice to stick around and deal with the fallout, but instructive about yourself, too. So gains can be made, in either case.
I do think one of the most important considerations you have is just how short your relationship was before you married (and still is), which makes it harder to determine if real and lasting change is possible. I had many good-to-decent years (albeit full of warnings of things to come) prior to meltdown to keep me hopeful now.
Whether or not he may have NPD, your husband certainly has a lot of issues with responsibility - both corporeally (like with money) and personally (passing the buck, minimizing his own faults, rationalizing his behavior). Mine did, also, but has improved tremendously in these areas since the Year of Our Damnation. Other probelms, not so much - but baby steps happening.
Potentially, that means a lot of "mothering" in your future. Only you can really determine his potential for growing up to be the man you want to be with.
Deciding to stay can be benevolent and kind, but can also be enabling. There is a little "relationship geometry" and "inner-world calculus" yet for you to do, in my estimation.
See what fruit therapy bears; there is no rush to decide - so long as you know you are in the process of making a reasoned, self-valuing/respecting decision rather than acting on an impulse to save a fantasy or avoid your own issues.
T