15 yr old Son wants to live with dad and aunt because better school but I Have sole legal custody, can I allow him to do this without losing custody?

My son is 15. I feel cornered into this decision because they have told my son that I live in a "bad city and horrible school district." For years they've have told him every visit that he should move up there because it would be so much better for HIM. (His father is 20k in arrears, has told our son that it is on purpose) The first few years, I said NO to this. But since the age of 12, he has developed a good relationship w/ his Dad, and I encouraged this. Always. I have sole LEGAL custody. Can I "allow" my son to reside with his Father (and subsequently his Aunt (who is wealthier and no younger children to care for, like I do) so that he may receive a much better High School education, without losing custody of my son? However I personally feel towards them, I have known he would need his Dad, more, someday. But I still want to retain the right to bring him back if this school/visitation w/ me/his siblings if this doesn't work out! I raised him ALONE for the 1st 7-8 years!