Being faithful or sexually exclusive with one partner is a decision.
The best way to stay faithful when your tantric sex desire wakes up is to have the best and most fulfilling sex with your partner.
Dialogue is again a key ingredient to understand the dynamics you face.
You might have fantasies involving other persons that your partner.
These fantasies are okay.
You don’t have to act on them.
This is the key issue.
If you feel a desire waking up, see what happens when you express it directly with your partner.
Now, if you want your partner to stay faithful, you need as well to offer him or her an avenue of expression for their desires.
If you tend to block, suppress or judge what comes up, you might stimulate him or her to go and look somewhere else.
Of course, never engage into something you really don’t like.
Talk about differences or tensions if they arise.
You will discover that having a protected space to share all this is often all you need to understand your next step.