Yes, that has potential disaster since you aren't thrilled about it. Did you discuss with her WHY she wanted to close and become monogamous? If so, do you think they were healthy reasons or fear based? If you are only agreeing because it's easier than stating your own hopes and desires, speak up now before you've broken both your hearts please?
Always the possibility you can negotiate what you want to both of your contents if you're upfront and honest about mismatched needs.
Happiness will never come to those who fail to appreciate what they already have.