Actually, there is a different way of looking at this. The flirtatious behaviour is something that if you practice in your marriage over time, actually engenders the desire. It is called reactive desire, rather than spontaneous desire and is how lots of long term relationshipskeep the sex intersting and alive even after spontaneous desire fades, as it does after the early stages of a relationship for many people, particularly women
The problem is that sort of flirty behabiour needs to be a regular normal part of your marriage before you get to the point where it is awkward.
A good sex therapist might help but it may be too late. Was there ever a time when you both really did have chemistry or spontaneous sexual desire between you? If yes, then there really is hope that you can get it back if you both want to. It will take some honesty and work though.
If the attraction and spontaneous desirer was never there in the first place, then that may make it a lot more difficult but you both need to be happy with this going forwards so honesty is also important here if you want a marriage that will actually survive long term .
Alternatively, accept that one of you is likely to meet someone else and/or leave at some point, when a sexless marriage no longer serves your needs. That may be a while yet though so you can of course continue as you are and just hope the marriage survives a while longer, it may well do