To be faithful is to be loyal, devoted and staying true to your relationship. It equally means that you trust your partner regardless of physical attraction or lustrous desire you could get for someone else.
Being faithful requires that you stay emotionally connected to your partner, that you find ways to revive the burnt out flames of your relationship and it also requires that you stay content with the person you are dating.
Faithfulness like abstinence is a tough choice seeing that you get to see better behaved and more physically attractive but it is a choice one should make everyday within their relationship.
You can stay faithful by addressing any problems, not making comparisons between your partner and anyone else you could be attracted to, coming to terms with imperfections as well as communicating more often about fears, expectations and just to keep tabs on how your other half is doing