Sex with wife is ur birth right. Sex is must for good mind , body and soul ( for other then Tyagi's).
Not joining means what ?? She is not living with u or not physically participating though in bed.
If she is not physically indulging then talk to her, talk thru her female close one, take her to gynec ( she may be getting pains, and other issues) , finally go to a good lady s*xologist. Ican recommend few if needed.
In the mean while like even mor ( peacock) does keep her happy, have good bath , have privacy, light music etc before going in bed. You can take lessons on love making from a good authentic s*xologist or relationship experts.