My partner was on a night out with some friends, one of whom was the DH of a friend of mine. They have young kids together. My partner saw him get flirty with a girl, who then sat on his lap, they got touchy-feely and proceeded to kiss. My partner confronted him about it, and he brushed it off and undermined him, implying it's just the way it is/as though he does it all the time. Now I don't know whether to tell my friend, or not to meddle in their relationship. I feel so bad for her, and it's awkward carrying this information. Any advice?