Not an apt simile. We are talking about a partner who wants other sexual partners and you did not answer the question.
I did, and it's not a simile. It's an instantiation of what you said you wouldn't put up with: A partner who is looking for other people to do some exciting activities with you can't offer them. And, hey, a climbing buddy is someone you're entrusting with your life. That's more than you can say about a lot of varieties of sex.
If you prefer a more direct answer: As long as I can be sure that there are things my partner only has in me to balance what is lacking in me.
If you think the emotional bond formed during rock climbing compares with that of sex, rock on.
I speak from hard earned experience and hard learned lessons. The view from the top of the rock face gives one a different perspective.