。
I won't abandon you.
Literal
I [topic-は] not-abandon.
見捨てる (みすてる, 'to abandon, forsake') — a compound verb from 見る ('look') + 捨てる ('throw away'). The negative ~ない is a firm declaration of loyalty. The object (the person not being abandoned) is omitted — context supplies it, as is natural in Japanese.