Lex
I am amazed that he opened up and shared feelings with you! Teenage boys are notorious for responding with single words!! The distance you are feeling right now may be a defense mechanism for both of you. You've been hurt by being withheld from him. I'm sure that he was hurt as well. Neither of you want to feel that pain and the best way to do that is to not make the connection again.
It's going to take time for both of you. But the closeness that you shared up to the time he was 11 years old will return if you both work on it. And it sounds like you are both willing to do that.
The love that a mother has for a child runs deep. The love that a child has for their mother runs deep as well. It's there.
gentle hugs
And the fact that he loves animals shows that he has a compassionate heart. I have great hopes for both of you!