Hi Rita,
You can place a request with this website
www.familyulster.com to look up in the Irish GRO Death Indexes.
Also, you can do the same with the Marriage Indexes.

Or the quickest way to find the marriage registration is to check the excellent database on
www.emeraldancestors.com where you can view many marriage registrations from 1845 and up to 1925/30 (they do have some early parish marriage records as well). All of this for a tenner--a good value for your money if you want to find more on other family members.

Do you know if your Patrick was a farmer or a landowner? If so, you can always check the Griffith's Valuations to see when he "disappears" from the records (usually means a death or sold the land off).
I wish you the best of luck in finding the information on your ancestors!
Kind regards,
Tees