Is my ex married to the girl he is dating? I still love him and share a child with him. He admitted to having sexual relations with a girl. She said, before having sex with him, that she didn’t want to have sex unless they were exclusive and committed. Well, he basically agreed by having sex with her. I told him that even if it wasn’t verbal, he agreed to her conditions. Could that be a sort of covenant made between them? Are they now bonded to one another for life like a marriage? Also in regards to Deuteronomy 24:4, would that mean that exes, who dated and then sought out other people before deciding to come back together, are off limits to one another?
Marriage is a covenant. "Yet she is your companion and your wife by covenant" (Malachi 2:14). Covenants are not casually entered into. These are formal agreements with vows made before God and witnesses and with records made to record the fact that the covenant exists. See Marriage Covenants.
Your ex-boyfriend had sex with another girl. She expected him to be committed to her, but that isn't a covenant. Basically, he lied so that he could have sex. As sinful as he is, he is consistent. He is willing to have sex with any woman who will let him. The fact that he has been committing fornication with you demonstrates that.
Deuteronomy 24:1-4 doesn't apply. It is an Old Testament rule that deals with a married couple who divorced because of sexual uncleanness (i.e. fornication). Best that I can tell from your note, no one mentioned has been married.
This gets to the core of the problem. No one is following God. Instead of waiting until after marriage to have sex, everyone is engaging in sex and pretending that this somehow is equivalent to an actual marriage. What everyone is involved in is fornication. "Now the works of the flesh are evident, which are: adultery, fornication, uncleanness, lewdness, idolatry, sorcery, hatred, contentions, jealousies, outbursts of wrath, selfish ambitions, dissensions, heresies, envy, murders, drunkenness, revelries, and the like; of which I tell you beforehand, just as I also told you in time past, that those who practice such things will not inherit the kingdom of God" (Galatians 5:19-21). If you wish to please God and reach heaven, you can only make it by living your life as God requires.