Lack can be noun. It means absence of something needed, or something missing.

For example,

• There is no lack of talent on this team. (phrase: no lack of)
• The team has a lack of skill. (phrase: a lack of)
• He felt the lack of a steady income.
• A lack of money prevented us from buying a house.

Lack can be verb. It means to be without, to fall short in.

For example,

• You lack common sense. (= you don’t have common sense, but you need it.)
• He lacks three votes to win.
• Nothing lacks but their full agreement. (= Nothing is missing)
• She will never lack for friends. (phrase: to lack for sth)

Lack is not often used in past tense. In stead, you can say:

• That’s what has been missing from my life!
• I’ve always wanted.
• I really needed this.