Uhmmm, if you have not been keeping saltwater fish and invertebrates for at least a decade, then please do not even think of keeping an octopus.
Octopi are relegated to the expert of the experts level of knowledge/experience.
I've been doing this for over forty years and still don't think I would want to hassle with trying to keep an octopus.
They have much more demanding water quality requirements, even more so than corals and they also need an environment that is designed specifically for them, and that goes a lot further than securing the lid.
Octopi have been known to die of boredom as well.
Just getting one and putting it in your average salt tank is just a death sentence for the octopus.
Tell your boyfriend he likes guppies.