Interestingly enough I've been having a simliar problem, but with regards to visits etc. My bf's explained already but I still don't get guy psychology on this front, so I went and talked to my ex lol and he explained it again, and I think I'm finally understanding this.
Guys and girls have different kinda expectations. I think maybe us girls start missing guys a lot faster than vice versa, hence we frequently contact whereas they don't. It's got nothing to do with whether they like you etc - it's just different expectations, different ways of doing things, different psychology.
Stop reading so much into it. I was convinced for 2 years that my ex didn't want to be my friend. Now recently we've been getting on quite well and he revealed how it had nothing to do with that. I don't understand it still, but I'm coming to realise that it's just a difference between being a woman and being a man. Lol.