You have a good relationship and want to protect it because you value it. That is what we do with things and people we value. The how becomes very important.
Relationships are incredibly challenging, why not put the odds in your favor?
What ways do you protect the relationship? Your partner?
Can you imagine a way to do an inventory or risk assessment, to see how vulnerable your relationship is to outside forces?
What ways does your behavior make the relationship more vulnerable?
Is the foundation strong enough to build upon?
In what ways are you signaling to your partner that it is okay to cheat, that it is not that important
to you, that you are not really invested?
In what ways are you letting them know that this is not a valuable relationship?
Consider talking with your partner about what reassurance you need, what facts you need, how much freedom and alone time you need, what you need in terms of fidelity, jealousy, anxiety and letting other people into the important areas of your relationship.