it really bothers me

It's came out recently that a member of my husbands family was having an online affair. Well his whole family not only sees nothing wrong with it they justify it. When I talked to my husband about it he said that his family memebers wife was a total bitch and the woman he was having an affair with was the only person who actually loved him. When I said that if his family member was that unhappy he needed to just leave my husband came back with "shit happens." Now it's really bothering me that my husband is that causal about an affair and really feels like it's ok because that woman loved his family member and well "shit happens".... what if he meets someone he thinks loves him more than I do? It's just going to be some shit that happens...? I'm really bothered by this and it's actually changed how I view my husband. This may seem weird or petty but as someone who's been cheated on and someone who is SOOOOO against infidelity it hurts me to hear my husband who told me was also against infidelity for any reason say "she loved him shit happens." Am I being overly sensitive or would you guys be concerned too?