What should I do in this situation?

In May, I asked my boyfriend of 4 and a half years to leave. He started being very distant and not spending any time with me and our son. At the beginning of July, his mum died and he turned up on my doorstep, claiming he had no-one else to turn to. To cut a long story short, we ended up having , I put it down to his way of dealing with his grief. In the morning, I caught a glimpse of a text message he sent to another woman claiming to be in love with her and wanting to be with her. I later asked him about it and he didn't deny or admit it. Last week, we took our son on a day trip and lo and behold, we had again. He said he would return later that evening, but I have not heard from him since. I have written him a letter because he won't give me an explanation as to what our situation is. I've said that I don't want to see him anymore, and it's time I moved on, although I still love him. Should I send it to him?