Help - Coparenting a newborn

So my sons dad has been sporadically visiting 2-3 times a week the last 4 weeks. My son is 5 weeks. The first week he was here every day, then it tapered off. One week he didn’t come all week then came three days in a row because he decided he was done with his gf and wanted to whisper all the sweet nothings in my ear. Naturally my hopes got up but a couple days later I had a bad feeling and checked her social media to find they were very much still together. Thankfully nothing happened between he and I aside from him kissing me and saying alllll the things. But still i was in SUCH a good place with everything and got thrown for a loop. Now i know how toxic that situation is and likely will never be able have a friendship with his gf which I was aiming toward since she would be involved with my son due to him having validated all her insecurities toward me. I’m having a hard time keeping my anger out of my interactions with him. Previously we had great positive communication but because of my intense feelings of anger I’ve been distant and short, not intentionally just in efforts to not let it all loose, you know? Plus I’m not in any way obligated to appease him and make him feel good about himself. He texts me “good morning Dawson” and i have no idea how to respond or if I even should. Previously I was sending a picture and saying good morning dad but honestly, I feel like this makes him feel accomplished and like he “saw” him and encourages him to miss time with our son. How would or do you guys handle interactions like texts to a newborn with the other parent who is willingly forfeiting time? I do want to keep it all strictly about the baby because anything outside of that is just playing on my emotions but at the same time feel like it’s stilly to say you’re going to visit the weekend then completely forfeit your time then text. If my gut is right he was too drunk or hungover to spend time with him which makes me more angry. He has the opportunity to see him every night but I’m feeling like we need to set a schedule so that he is held accountable and it’s not “when I’m not doing other things” but “I’ll do my other things when” you know?