Kisses.
Kissing Shelagh was like being in heaven.
There were many kisses over the years: surprise kisses, chaste, sad kisses, kisses of despair, kisses of thanks, or joy. Kisses to shut her up when she scolded him, or when she cried or felt overwhelmed by some situation.
Kissing Shelagh was his life, something he dreamed of and didn't dare to do until he knew she was his, that she loved him even if that sounded incredible.
Kissing Patrick was her vice.
She never had one but when she did it once, she knew she could not live without doing it all her life. At first she waited for him to approach, but eventually she learned to take the initiative and do what she wanted. She was always reluctant to physical affection, and much more if it occurred publicly and even more, in front of her children. With the passing of days shared with Patrick, she knew that the best thing she could do for the children was to show how much she loved their father.
Kissing was their way of communicating and loving each other, it was what they wanted for a long time and when they could do it, there was no reason to stop.