What does Donne mean by use myself in jest by feigned deaths to die?

In this stanza, the speaker is comparing his departure to death, noting that since he “Must die at last”, it is better for him if he practices dying by “feign’d deaths”, which are those short times when he is separated from his love. Thus, the speaker turns her fears about losing him into a declaration that she is the source of his existence...... when he isn't with her, it is like being dead.