How do I repair the damage done by a careless remark?

My son and I have had a troubled relationship throughout the years that has mellowed as he went into adulthood and stayed out of trouble. However, recently he hooked up with a girl he really seems to care about, and that I was totally unaware of until they moved in together. As a mom, I had some concerns about the girl but usually trust my son's judgment. However, recently my son moved back to the state I reside in (he worked out of state for 2 months) and I became frustrated when a week went by and he didn't come by to see me, so posted something to that effect on Facebook, and privately emailed the girlfriend and said she was always welcome, etc. because I didn't want his distance to imply that she wasn't welcome. Anyway, to cut to the chase, the online conversation with her deteriorated, with her bringing up my online comment, saying I did it intentionally to hurt my son, etc. I said that she missed my point, and that perhaps we should end the conversation. She made a nasty comment and signed off, then at the next family gathering, didn't look me in the eye or speak to me. The family gathering after that, she didn't come. Now for my careless remark. I had talked about this to an old friend who has a son the same age as my son. So after the no-show at a family dinner, I replied to a Facebook thread making a negative comment about the "skank". Long story short, I completely forgot the thread was originally a group thread and my son was in it. He read the remark, replied that next time I should watch who I am posting to, UNLESS it was done intentionally. I tried calling, texting, and sending an email. My friend actually realized what I had done and sent an email to him first, talking about "mama bears" watching out for their kids, etc. I have not received a reply from him at all. With our history of problems and a shaky relationship, I am of course, worried that he will totally break off all contact. I don't know what to do at this point.