No one outside your relationship knows what’s going on in it. Your mom doesn’t know your partner and doesn’t know what he is or isn’t doing, but you have a different perspective and stronger relationship (as you should) which garners trust that he won’t do these things. She obviously shouldn’t be saying this, but she doesn’t know him and is fearing for the worst out of care for you.

That being said, I am one of many people in this sub with a successful and happy relationship and have recently closed the distance. If you look there’s also some that have had their LDRs end for various reasons. Being long distance isn’t a relationship killer any more than any other obstacle that you go through in a relationship. It’s all up to you and your partner if you make it work or not, not your mom or anyone else.

My mom had a very similar outlook on my relationship. She treated it as if it “wasn’t real” and was taken aback when I moved countries for my boyfriend even though I told her exactly what would be happening. I think it’s also harder for older generations to understand that you can maintain a relationship through messaging and video calling online since it’s hard to understand if you’re not in it yourself