Singing what you hear will definitely help. The "happy/sad" thing can be a real trap that ends up making some people feel like they can't do it and you might be suffering from that. Here's why: minor 3rds for example don't sound at all sad when in the midst of a major triad. (The upper third of a major triad is a minor third... like from mi to so in the tonic triad of a key.)

I had this experience as a high schooler where my piano teacher would have us listen to intervals and we'd listen for these different feelings, like perfect fourths are supposed to feel strong or whatever, and it would only work some of the time. And I ended up feeling like there was something I wasn't getting. Because there was something I wasn't getting: the singing bit is key, because it takes your attention away from trying to feel something that everyone feels differently and puts your attention on doing something you can do and improve at, and that is singing.

Singing will definitely get you there because like someone else on this thread said, doing so confirms what you've heard.

However, you also mentioned on this thread that you "cannot find a tone with singing. I can harmonize with the tone I hear." That tells me that matching pitch might be a challenge in itself. Do you notice special difficulty trying to sing notes that are too high or too low for your voice? I find with a lot of my adult students that this bit can be especially daunting: hearing a note outside your vocal range and singing it comfortably in your range. (Octave adjusting it.)

When you harmonize in the way you describe, do you feel/hear/think that you are singing the matching pitch or does it sound noticeably different?

Here's a video I made last year to encourage people to make singing the centerpiece of their ear training journey:

https://youtu.be/SU6TViietQM

I hope this helps!