In a long-term relationship, it's just not realistic to have that OMG SO IN LOVE feeling all the time life is full of dull, boring, and unpleasant bits, like grocery shopping and having the flu and visiting relatives that you maybe find slightly tiresome. For those bits which is a lot of your life, honestly you need a partner that you like and enjoy spending time with, who you trust, who can support you, who respects you and is willing and able to be there. Sparks are great, but sparks are not the thing that makes one willing and able to support a partner through difficulty, or grief, or illness.
If you are in a committed relationship, you wouldn't be cheating to begin with. If you cheat and you consider your relationship COMMITTED, it's not a committed relationship to both people at all. When two people are committed to each other, they do not cheat. However, I do think that a cheater might be missing something in a relationship.
