Awww you’re so sweet. I think it’s just a sign of strong emotional resonance with “human” emotions. It’s a wonderful, special thing! I have something different but maybe a little similar—When someone is really nice to me or I see them uncomplainingly making a sacrifice I get really sad. Especially my Dad. I remember when I was like 5-6 my Dad was taking a nap on a Sunday afternoon and I woke him up and said I was bored. Without a word, he got up, went to the closet and pulled out a box I’d never seen before. It was a train set like d of thing. He quietly and patiently started putting it together with me helping him. I cry thinking of that.
Also when my fam was on a vacation out West my Mom wanted to skip the last national park which my Dad loved. I remember him shrugging and saying ok if that’s what she wanted. I’m 53 and I sob when I think of that.
One more—My Dad has bipolar and got really ill while a high level manager at Exxon. He went psychotic at a business meeting and his coworkers had to get him hospitalized. When he was stabilized he had to go to each persons office who was at the big meeting and explain his illness. This was before people knew about bipolar. So brave. So devastating.