OK, so he has form. Hence, your spidey senses are inevitably going to be off the radar which is absolutely understandable. Being devils advocate here, I get quite a lot of texts from a pizza company. It is not on my contact list. Having got fed up with texts, I replied "STOP" to prevent any further and then deleted the lot. Is something like this possible?
Can you get hold of his phone and let him think he's lost it? Does he take it to the loo, shower, down to the shed, that sort of thing ie : never lets it out of his sight? Is he disappearing off and not telling you where he's going, has his routine changed? Is he "working late".
You are definitely not going bonkers. Given the situation where you were prescribed AD's and were proved not to be bonkers, is he likely to react in the same way if you confronted him now? As you know, I have been down this road, I recall seeing a text on H's phone from an old work colleague saying "I love and miss you" or words to that effect (it was a man). I did actually believe it because I trusted him and had no reason not to. Now know it was from an OW not sure which one. H obviously laughed it off, told me I was "mad" that old chestnut and said it was just a joke. That got deleted pretty quickly!
I think you should get hold of the phone and see what comes in. Then confront him. Don't sit on this, it's hideous and stressful and you don't need that in your life.
You know where I am. Sending huge hugs xxx