What you describe is commonly referred to as having an open relationship with a DADT (dont ask don't tell) policy.
This is a common way to come into poly, but it is not poly if you intend to have a sexual affair. Have you discussed what you would like to do if you fall in love? Its highly possible if you follow through on sex with others. Having some ideas on what you will do might help, although none of it might turn out the way you think.
Love is all encompassing and not easily abandoned if that is the boundary you choose. Remember what it felt like to fall for your husband? Powerful, overwhelming, incredible, beautiful. Having sex with others could bring that up again. If there is at all a chance you could fall in love, either don't go this direction at all or discuss options around having other partners.
Do some reading here and see what you find. Look at the search engine under tags and see what catches your eye.
Mono's movie suggestion is an excellent one!
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