It’s “possible,” but as of now “highly unlikely” due to the fact that “he’s with someone else.” You don’t say what is meant by that, but if he is “married” he could hardly be the soulmate that God has prepared for you. We need only go back to the first “two soul mates” to see this. In Genesis 2:21-22 we read, “And the LORD God caused a deep sleep to fall on Adam, and he slept; and He took one of his ribs, and closed up the flesh in its place. Then the rib which the LORD God had taken from the man He made into a woman, and He BROUGHT HER TO THE MAN.” We often hear the expression about a married couple, “Those two were made for each other!” and this was literally the case when “God made Eve for Adam.” And because God made them for each other “He brought her to the man.” Again, this literally happened, for after Adam was awakened God presented the woman to her. It is very striking to see what Adam’s response was for he said, “This now bone of my bones and flesh of my flesh,” and the first marriage took place.

We learn a very important truth here that you should think about; Adam KNEW that “God had made the woman for him.” In your question you said nothing about what this man thinks of you. Again, if he is married this is a moot point for the Bible says, “Therefore what God has joined together, let not man separate” (Matthew 19:6).  If you were to pursue him, you would be guilty of possibly breaking up a marriage! But even if he is still single he is obviously in some kind of relationship with this woman and thus it seems highly unlikely that he is interested in you, and he certainly isn’t thinking, at this point in time, that “you were made for him.” You must come to face the fact (again, at this point in time) that he is not your soulmate while he is currently “with someone else.” Could that change? It could, but you must not force the issue. If indeed he is “the one that God has made for you” his relationship with her must come to an end and then he must come to the same conclusion that you seem to have come to, that “you are the one God has made for him.”

I could end my answer here, but I want to address one more vital issue. You say that he is the “person you want, physically and personality-wise.” You say nothing about his “spiritual state,” which, if you are a true believer in the Lord Jesus Christ, should be your FIRST PRIORITY in a soulmate. The Bible is crystal-clear that a believer should MARRY ANOTHER BELIEVER! In 2nd Corinthians 6:14 the believer is told, “Do not be unequally yoked together with unbelievers.” For one to be a soulmate they MUST share your same faith in the Lord Jesus Christ. In addition to being a true believer, they should also be SUBJECT TO CHRIST AS LORD. Paul taught this in 1st Corinthians 7:39 when writing to widows, “A wife is bound by law as long as her husband lives; but if her husband dies, she is at liberty to be married to whom she wished, ONLY IN THE LORD.” If these two things aren’t true, there would be conflict in the marriage, for we read in Amos 3:3, “Can two walk together, unless they are agreed?”  (410.3)  (DO)