
All in all, communicate with him, see where your future go with him. If he avoid the "marriage word" like a plague, he is not ready to make that kind of commitment. If he says "sometime in the future", set a time limit for yourself the time, like a year or five years but don't hang around for so long waiting for it. If you want something more, and he isn't willing to get there, either you settle for "partner for life" or move on.
As for your grandma's ring, can you get a jeweler to make a carbon copy of it? Then you can put your grandma's ring in safe keeping. It may cost you a bit more but it's a lifetime of wearing. I bought a stainless steel Celtic ring on Ebay and I love it! Better than my wedding ring that I kept smacking against surfaces would flatten and it split the seams. With this stainless steel ring, I never have to worry about dings, and bends, or splitting. I believe it is made of titanium steel.
As for the tat, its your body, and your money, go for it!