The Old Testament does restrict re-marriage to your ex-spouse. Under the new covenant no such restriction is given. The only restriction to remarrying your former spouse is if either of you are married to another individual. If one of you is currently married, you should not seek to destroy or divide that relationship.

If neither of you are married you are free to re-marry one another. Grace rules in this matter.

Deut 24:1-5

"When a man takes a wife and marries her, and it happens that she finds no favor in his eyes because he has found some indecency in her, and he writes her a certificate of divorce and puts it in her hand and sends her out from his house, 2 and she leaves his house and goes and becomes another man's wife,  3 and if the latter husband turns against her and writes her a certificate of divorce and puts it in her hand and sends her out of his house, or if the latter husband dies who took her to be his wife, 4 then her former husband who sent her away is not allowed to take her again to be his wife, since she has been defiled; for that is an abomination before the LORD, and you shall not bring sin on the land which the LORD your God gives you as an inheritance.

NASU

Jer 3:1

God  says, " If a husband divorces his wife and she goes from him and belongs to another man, will he still return to her? Will not that land be completely polluted? But you are a harlot with many lovers; Yet you turn to Me," declares the LORD.

NASU