The reason why he reached out doesn't matter. If you even try to think why he does things you are going to drive yourself crazy. You must learn to accept and then let go. That way you don't have to decode, decipher, decrypt, decide, what he means when he says things. You just take a deep breath, accept that your X reached out and then you let it go. You let that go along with all the anger, fears, wants and needs because at this point. None of it matters in your life. You are doing fine without him.
And another point I want to say. If you have this many questions, and if your blood pressure goes up that much and your heart starts to race just from him texting you, then its pretty safe to say that you are not ready to see him or talk to him or communicate with him in any way. You never talk to your X when you are at your lowest point.
So my advise would be to just let it go. If he reaches out, you read it and then delete it and accept that he did and think nothing more about it. Let go..