I think I might be a little confused...and my answer is going to go a bit against the grain.
I'll start by saying that I think your picture is adorable! I also don't think, in general, that there's anything wrong with keeping a new relationship under wraps. Especially in the beginning when you're still exploring your feelings for each other. When I first got together with my now DH, we didn't immediately tell our friends what was going on. We didn't make a huge announcement, but we did eventually start being more open around our friends. Holding hands and then admitting that we were together. But, I don't think there's anything wrong with "announcing" the togetherness either.
Unless I'm missing something, I can kind of see why the friend had a strong reaction to your particular situation and I hope I can explain it well. When I first saw the picture, I thought you were announcing an engagement. I had to go back and re-read the thread to find out that you were just dating. And while there is nothing wrong with announcing an engagement, the quote itself does seem to kind of slam the ex-spouses. Since the divorces are recent, if the friend is at all close to your ex, I can kind of see why he had a negative reaction to it. Maybe it was like his initial reaction was that this new romance overlapped with the ex and/or you were rubbing it in the ex's face.
Now, all that being said, if that is what he was thinking, he could have explained it to you and you could have explained that he misunderstood. Depending on the situation, this might be something that would set me aback, but I wouldn't end a 10 year friendship over it!