I don't know how I feel about my baby boys name anymore😔💔

Sierra
Me and my boyfriend just found out that God has blessed us with a sweet little baby boy. Me and him both agreed before we told anyone I was pregnant that if it was a little boy we would name him Mason. He told his mom, she said that we couldn't name him Mason because her friends daughter is having a baby boy and naming him Mason... I was like well okay, we can figure something out. So many, many, many many baby boy and girl names later we had finally chosen Addalynn for a little girl and fell in love with that name and still proceeded to look at baby boy names because we didn't know at the time. Oh and keep in mind that every single name I have tried to pick out for our son, my boyfriends mom has either had someone's childs name that she knew and she was close to them and told me that we just couldn't name him that. So the day came where me and my boyfriend were sitting down and discussing what we should name out boy and.i had looked on a baby sight sometime last week and seen the name "Kayson". As soon as I seen it I fell in love with it and knew it was absolutely perfect for him. He had brought that name up and made me fall in love with it even more because it was a name we had finally sgreed on! I begged him for us to keep it because he kept telling me that it was just too early that we will probably find something else but I loved this name way too much and knew it wouldn't change.... The next day he went in the living room and told his mom the news about is finally naming our son and said, "that's gonna be my godsons Sons name...." I flipped sh*t.... She sent me messages on Facebook telling me she was sorry but it was disrespectful and that we couldn't name him that but we could name him Mason?!?!???? Me and my boyfriend wouldn't even have been looking at other names if she had let us use Mason but I'm done seriously. I'm beyond upset... I say there and cried and cried over my little boys name because I feel obligated to name him something else and I just don't want too... She got really upset when I told her that I wantted to keep it... Not every woman is going to name her child something so uniquely  different that no1 else is going to have that name on the face of this Earth! I don't wanna change his name and it's not like we knew that her god sons little boy was going to be named the same thing.... I don't know what to do, I'm scared that if we keep the name then later on it will cause conflicts with her and I really do not wanna start anything else with this woman we are just now getting on good terms! I can't find any other baby boy names that I absolute feel is right other than Kayson, and it's been 2x as harder because it's like nothing fits him now... I just don't know what to do, my mom said name him whatever me and my boyfriend want too that it shouldn't matter that much that I shouldn't be so upset about it but seriously every name I have picked out for our son someone else has had something to say about it.... I shouldn't feel like this about "my sons" name. He is MY SON! I'm just terrified...Â