Intuitively, are you able to visualize a 3 dimensional curved surface (analogous to a two dimensional curved surface of a balloon)? If you can't, then your intuition is failing to help you understand the geometry of the universe and you must learn about a reality that is different from what your intuition tells you. Heck, if our intuition was always right, what would there ever be to learn?!
Trying to understand the baloon analogy would be a big help here.
Ok....well think about how the concept of nothing could apply to the expansion of the universe. You're talking about a spherical universe with an edge and a center, expanding out into empty space surrounding it...... so where is this edge? Why don't we see it? Why don't the velocity vectors of galaxies have a preferential direction?
Actually, the concept of "nothing" really isn't abstract, but people often use imprecise wording that improperly frames the concept. For example, your quote:
...is an improper paraphrase of what people are telling you. They didn't say "space is expanding into nothing", they said space is not expanding into anything. These are two very different things because when people hear "nothing", they think "empty space", but the reality is that the universe is not expanding into empty space.....and empty space wouldn't be "nothing" anyway!