Believers that adhere to “Jesus only”

To my fellow believers that adhere to the teaching of “Jesus only” doctrine. When I became a Jesus follower in 1977 I worshipped for some time with the UPC in city in Texas as I was traveling with the USAF. As a new believer I had not came across the doctrine of “oneness”. After several months and seeking the Lord about this I had questions as to some verses that revealed that “there are three that bear record in heaven” (1st John 5:7)

One verse was from Jesus discourse prior to his murder. He speaks that he, the Father and the Holy Spirit as being separate entities and being in separate places after his death. From John 16: 5 “I did not say these things to you from the beginning, because I was with you. 5 But now I am going to him who sent me, and none of you asks me, ‘Where are you going?’ 6 But because I have said these things to you, sorrow has filled your heart. 7 Nevertheless, I tell you the truth: it is to your advantage that I go away, for if I do not go away, the Helper will not come to you. But if I go, I will send him to you. 8 And when he comes, he will convict the world concerning sin and righteousness and judgment: 9 concerning sin, because they do not believe in me; 10 concerning righteousness, because I go to the Father, and you will see me no longer; 11 concerning judgment, because the ruler of this world is judged. (ESV)

Please explain how Jesus could be just one. Other verses also show separate entities aka persons.