I think a big issue is that you are questioning his choice of partner, and turning it into a "me vs. her" kind of battle. That is not at all fair to put your son through; he does not deserve to be put in the middle like that.

You ask if his lack of contacting you could be "her influence", I would say not at all. He is an adult and can make his own decisions. The only bad influence I see is your outright dislike of her, which is probably making your son feel very uncomfortable and keeping his distance from you. Try to think of things from his perspective. He loves you and his partner very much, and doesn't want to choose between the two. That is very rough indeed!