Why do some (I cant say all) men after they made the vow "Till death do us apart" lurk for an external sex partner? Is there any explanation to that? It is keeping me from signing up on a relationship :)

This was written to answer another question, but the answer still applies to your question:
http://features.beliefnet.com/areasontosmile/2011/11/qa-why-do-all-guys-cheat.html and you also might take a look at how guys *really* think:
http://features.beliefnet.com/areasontosmile/2011/10/understanding-mr-right-or-how-to-train-your-husband.html

Ask me anything