I so get being wary of an ex-spouse's boyfriend/girlfriend butting in on the parenting front! I have spoken with very dear female friends about this topic, learning how they feel about their ex-husband's girlfriends, learning what girlfriends do that hurt/upset my friends, so I know better what to do and not do. When I'm dating a man with kids, I feel very aware of how his ex-wife must feel, thinking "She's like my own friends, worried about this new influence in her kid's life."

I'm better at speaking up now when I'm affected by something, but like you I agree it's not my role to give unsolicited parenting advice.