This happened to me recently. My Patron Goddess was always Demeter. She was there as a mother figure to me when my own mother was not. I could always go to her and she would comfort and guide me gently. Once I was able to care for myself and my emotional needs more she slowly faded into the background, not missing mind, but there when I needed her. One day I started feeling another presence in my mind, making more and more noise as time went on. One day I could no longer ignore it so I opened my heart and mind and found out that Aphrodite was calling to me! I know now that Demeter was slowly backing away so that I could accept a new Patron in my life. And while I know that if I truly needed her Demeter would be there, Aphrodite is now my new Patron.
I think that atonement is a good idea, at least as a way of apologizing for being away for so long. But see if you are being pulled into a new direction.
A very good personal example. I had a somewhat similar example except I didn't have such a long relationship with my first patron.
I was initially called to Hellenic recon by Apollo followed shortly after by his twin Artemis. However, as I came to be more familiar and comfortable in my practice I began to feel Artemis pulling away a bit at a time. It wasn't long before I felt a little uneasy that my patron was already leaving me more alone with her brother. However, it was not long until I felt a pull from two new Gods. Both Hermes (whose sphere of influence links closely with my job) and Dionysos (whose links with freedom and madness reverberates well with me) began to make their presences known in my life. I know I can always ask Artemis for her guidance, but those three Gods are the closest to me at this time in my life.