I had the same thing happen with W's best friend (post MLC). She is only 24, and was smitten. She wanted to go to a few sporting events with me and my friends and then tried to instigate something more serious.
She has been one of my biggest supporters, so I had to nip it in the bud. I could only see huge problems ahead. As this guy is your H's friend I can only see problems ahead.
IM'ing is okay, a bit of fun, and hopefully he saw it the same way.
Don't feel bad.
AndyV M38 W36 D7 M 13 years Together 17 years W wants D mid Dec 06 (ring off) W wants separation early Jan 07 (she backdated to Oct 06) EA revealed end March 07 (Nov 06 W first meeting with OM) Hallmark moment "I care for you but am no longer in love with you."