You yourself used the word "depressed." He got help a while back; now it's time for you to get help yourself. You were all in favor of his getting help, so be in favor of it for yourself too.
Your following up with "a nasty text message" indicates you couldn't control that impulse -- and controlling those impulses is something we have to do, or how will we teach kids to do it?
After you apologize to him -- yeah, that is something you should do, even though he is overreacting -- tell him you are on your way to see a doctor and get a full screening for depression symptoms and would like to have his support. If you are indeed depressed you can't deal with it alone; you need a professional to help. And you also need his support. You weren't clear if you live together or not, but you do have a child together and will have to interact on things related to your child. At a minimum, he can communicate with you and get past this one incident. At the best, he and you will continue as a couple. He may not realize that you are ill (which you are if you are depressed). Once he "gets" that your illness was talking and not you, he should support you as you supported him through his issues.
And both of you together could look into couples counseling and parenting classes since there seems to be a lack of communications skills. But first, see a doctor about depression. You want to be at your best for your child and depression prevents that.