First here is a posts about cheating since cheating can happen in these types of situations.
Aries tend to be honest people and will probably tell their partner what is going on and get ready for a break up. But the thrill-seeker in them might stay in the relationship while pursuing the person they like so they can have physical benefits and some excitement. But this probably won’t last long and the truth comes out quickly.
Taurus might not know what to do if they are in a relationship and then start to have feelings for someone else. They can feel torn between the comfort of their current relationship and the attraction to another. They are likely to spend time with another person until they are 100% sure that their crush likes them and wants to be with them and then they break it off with their current partner.
A Gemini can be a bit of a tornado when it comes to this kind of stuff. Typically they will leave a partner if they start to like someone else. But usually their problem is that they like multiple people. Gemini might go back and forth between two or three people. An extremely undecided Gemini can fall into possible cheating habits but usually if they cheat it is not in a physical way but with communication, flirting, and an emotional bond.
Cancer can feel really guilty for liking another person when in a relationship. They might suppress their feelings until finally something has to be done. This makes it so they might leave their partner unexpectedly and hurtfully.
Leo will probably be very “in the moment” if they like another person while in a relationship. Spontaneously leaving their partner or even running off with this other individual can happen.
Virgo, the over thinker of the zodiac will of course mull over what to do if they like someone else when taken. Eventually they will come to a conclusion and will explain to their partner what has happened.
Libra can feel very uneasy when they like someone else while taken. They might deny their feeling for a bit or try to force feelings. They might test the waters with another person until they are sure about how they feel and their crush feels. From there they will leave their partner.
Scorpio can have a lot of inner turmoil when put into this situation. Eventually their heart will pull them where they belong but until then it is a inner war (however their partner might not know about this until the end). A perceptive partner might be able to end things quicker for their sake or find a way to instill passion into the current relationship (which Scorpio might secretly want).
Sagittarius goes with the wind on this one. As soon as they have feelings for another person they engage with them. Remembering to break up with their current partner is a different story. A Sagittarius can get caught in a sticky situation if this happens but due to their honesty it is likely an aware and considerate Sagittarius will let their partner know quickly that they are now an ex-lover.
Capricorn will IMMEDIATELY leave if they have feelings for another person. But this doesn’t happen often with Capricorn. They are usually picky about a partner and when they fall they fall hard so they aren’t the one to fall out of love with a partner or be tempted by someone else. But a Capricorn who is secretly dating a partner for something other than love…. that is a whole different story. This can make a Capricorn appear distant and the usual “faithful” to a fault trait doesn’t apply here.
Aquarius is prone to cheating if they have feelings for another person while taken. But Aquarius is also the type who might try to make things into an open relationship for their current partner and new lover. Aquarius is ultimately a communicative and honest sign. They won’t keep secrets for long if at all. But their unpredictable nature makes things an interesting ride when it comes to this type of situation.
Pisces will try to find the most tactful and easy way to break up with a current lover when they have feelings for someone else. For a Pisces to do this they have to really be in love or swept away by someone else.