It sounds like whatever it is that's gone on.. your son has in fact distanced himself. Could it be from the divorce?

Your son doesn't need to know if you seek out therapy to help yourself. Although you might wish to explain to him why it is that you said your mother - because it's your mother who you go to for help with your troubles. And make sure to explain that that's alright - because you shouldn't really be putting your problems onto your son, so it makes sense to rely on your own mother more in that regard. And then also explain that it is hard to feel close to someone when they have up such a cold wall against you, like he does.

He might be alright with things as they are, but you could still ask him if he would be willing to spend more time with you doing things that you both enjoy. He might be up for it, he might not. If he's so distanced and disconnected from you though, you really just might have to accept that.