New and need encouragement

[Not Quitting]

So now H is blatantly lying to me. Told S13 and I he was going away for a boys' weekend. He knew I was taking S13 away for weekend and where we were going. So what happens - we walk around the corner and who does S13 see but H and its not the "boys" he's with - nope it's OW. She walked into store and H gave S13 a hug and asked how his day had been. Not a word to me.

Now I've got S13 upset because his dad ignored me and he also wants to know ago the blonde was that his dad was with. For now I've just said I don't know and I've also calmed him down over the ignoring bit. S13 is now saying that he loves his dad but he doesn't want to talk to him. I don't want to come between him and H but I've got to defend my son's feelings as well.

This whole incident has also made me question my resolve to stick with my M. Any suggestions as to how to handle all this would be great.