@Jonny wishbone,
I'm not going to downplay the importance of sex in a marriage. It is an integral part of the bond between two people.
Having said that, you must be aware of not only the physical changes a woman goes through during menopause but the mental component as well. You don't mention any particulars, such as hormone therapy or hot flashes. Losing interest in sex is quite common. She's not alone and neither are you.
The worst thing to do is to bring up getting sex elsewhere. Please think through ultimatums such as that. You may get more than you bargained for. You talk about it's been a year but you also need to understand this is for the rest of her life too. Maybe she needs counseling, maybe you do too.
It all boils down to the level of effort from both of you. Both of you need to compromise and only you know what you are willing to do or not do. Just be aware, the grass isn't greener after a divorce and cheaters don't fair well either.
It's not that you have to suck it up either. But a little patience and a whole lot more understanding could be useful at this point.