One of the most important things in every relationship is trust, and that is why it is crucial for our partner not to let us down and to be faithful as long as the relationship lasts.
Considering the fact that people are different and that everyone has their own habits, desires, characteristics, we can't know for sure whether your partner is going to be faithful and devoted, but what we can do is tell you who is considered to be the most faithful according to the horoscope.
Scorpio and Leo may be the most possessive, but Capricorn is the winner when it comes to being dedicated and faithful. Capricorn is the most faithful sign in the horoscope, mainly because they don't see cheating as something physical but as a spiritual betrayal. They can be fascinated by someone, mainly with their intellect, but nothing more than a flirt is going to happen.
If they do cheat, they do it in the same way Virgo does, affair represents escape from the relationship. As much fidelity they give, that much they expect in return, so they never forgive cheating.