There is never an acceptable excuse to have an affair. Being miserable or having a bad marriage are not excuses. If it's really that bad, do the honorable thing and get divorced (or get counseling) before you start skanking around behind your spouse's back. Having affairs destroys families and has a trickle down effect to others, not just those directly involved. If you're still looking for excuses for why people have affairs, how about just admitting to having very low morals and being a *******.