Most Helpful Guy
There are a couple of things that could be going on here. Now that you and her are in an established relationship it could be that she is like most men in that she doesn't feel like she needs to communicate every hour. I think 90% of the non-porn site traffic on the internet is women messaging each other, she seems to be somewhat more like a man in that respect.
Another possibility is that she is desperate to end the relationship with you but you are coming across as so needy that she's afraid you'll jump off a bridge or something.
You have my deepest condolences on being a widower, that must have left a huge hole in your heart. To have two children with someone you love and them have them die unexpectedly, that had to have been a real bear to deal with. It could be that you are trying to hard to have her replace your wife, you're waning her to be the same person your wife was to get away from that feeling of emptiness, she loves you but she's just not had those experiences with you, the marriage, the children, all of the things you shared with your wife and probably feels pressured - even though you're not consciously trying to do that.
My suggestion is that you attend some sessions with a councilor and make sure that you are in fact ready for another marriage. It is quite clear that's what you want, but before you put your children in a situation where they could lose another mother, you had better make sure that you appreciate this woman for who she is, not for who you want her to be.