Lovable is the more common spelling of the word meaning pleasing or worthy of being loved, and the fact that it is more common makes it the safer choice. Loveable is not wrong, however. It is approximately as old as lovable (both are many centuries old), and it appears regularly throughout the English-speaking world.
Loveable is less common in the U.S. than elsewhere. The ratio of lovable to loveable in 21st-century British news publications, for instance, is about 2:1, while the ratio in American news publications is about 25:1. In any case, lovable is preferred everywhere.
Though lovable is more common, both forms are easily found in all sorts of writing—for example:
First, behavior is lovable behavior only if its agent is commendable for the behavior. [Moral Responsiblity, Authenticity, and Education]
Moving from a womanising thief to a loveable rogue, Tarmey gradually discovered Jack’s softer side. [New Zealand Herald]
These blue and gold cuff links are a way to support NASA astronauts and your lovable space enthusiast. [LA Times]
But what makes Stoic friends loveable and capable of giving love is the excellence of their
characters, nothing less and nothing more. [Thinking about Friendship]
Global self-esteem consists of two components—feeling lovable and competent. [Journal of Social Service Research]
Loveable greengrocer Gregg may be a hit with the housewives but ever since he met wife Heidi, he has been off the market.[Scottish Daily Record]