Llyr is quite unique and interesting! And just because you're not both 100% now doesn't mean it won't grow on you a bit. And it might fit your new son perfectly. Have you considered
Leary too?
Desmond is a very nice name and you wouldn't have to use
Desi as a nickname would you? You could use
Des or not use a nickname at all.
The names on your list are very nice!
Sebastian is lovely and
Ciaran is a particular favorite of mine. But overall I'd say
Ronan and
Llyr or
Ronan and
Desmond sound really nice together.
Hope you're able to come to an agreement. But it's always perfectly fine to take your list of name candidates to the birth with you and decide after he's born.
My Name Blog:
NameEnthusiast.blogspot.com