Hallo everyone

I don't really have an issue (or problem) yet, but Ive read a lot about stepfamily blending n all and Im trying to prepare the best I can for those future moments.

Being a fiancee to the man who has three almost teenage kids - I am stepmom to be. I love my future husband to be - very deeply.And I am aware what it takes to enter the family as a new wife and childless stepmom.
He hasn't divorced BM yet,but they are living separately for like 5 yrs now and she is living with a new man in her house.

My future stepkids are living with their mother but spending most of their time with their father,my future husband.
And I haven't met them yet,which is understandable - my man is very caring and thoughtfull towards his kids and he decided (very correctly in my opignion) to gradually introduce me and our relationship to the youngsters.
So they know about me and are guessing that we are gonna get married,because I am the first woman ever mentioned in their father's life since their parents got separated.

Recently I was talking with him over the phone when his middle son (age 12) told him to tell me that he said HI and - quote "you are too late,he already has kids".

I am living with my sister and her kids who are approximately same age as his kids,so its not that I don't have a clue about children even thou Im childless myself.I am aware of how being a stepparent is hard and I am now trying to learn and understand the most I can about all of the possible aspects of taking on the role od stepmom in order to create the marriage which will not harm the little ones in any way.

Of course,I had to give some kind of reply (cause kid was waiting for my answer and I simply said to my man "tell him that its totally enough for me that I can just love their daddy".

I know those are first steps into stepmotherhood and no one can guarantee what will happen when kids and I finally meet and how thay are going to accept me as, but I gotta ask was my answer right for a 12 yr old boy and what was the reason for his message to me...I wonder.

I am not sure was that kinda rejection from his son in the very start or fear that Im gonna take away their dad or smth.like that?

Did anyone had a similar situation?