In other words, you want justification?
Below is an example from a post on the old forum.

1. // justify one line of text
2. void linejustify(String s, int x, int y, int w) {
3.   // how long is the text?
4.   int tw = int(textWidth(s));
5.   // is it longer than expected width? if so, return
6.   if (tw > w) {
7.     println("Text is too long.");
8.     return;
9.   }
10.   // does it match perfectly? if so, print it
11.   if (tw == w) {
12.     text(s, x, y);
13.     return;
14.   }
15.   // if not, how much pixels shall we add to reach expected length?
16.   int gap = w - tw;
17.   // split the text into words
18.   String[] tokens = split(s, " ");
19.   // is there only one word - or no word at all? if so, print it
20.   if (tokens.length <= 1) {
21.     text(s, x, y);
22.     return;
23.   }
24.   // otherwise,
25.   // we will distribute the missing pixels after each word, in the spaces
26.   int spaces = tokens.length - 1;
27.   int[] pixelsToAddAfterToken = newint[tokens.length];
28.   for (int i = 0; i < spaces; i++) {
29.     pixelsToAddAfterToken[i] = floor(gap/spaces);
30.     if (i <= gap%spaces) pixelsToAddAfterToken[i]++;
31.   }
32.   for (int i = 0; i < tokens.length; i++) {
33.     text(tokens[i], x, y);
34.     x += textWidth(tokens[i]) + textWidth(" ") + pixelsToAddAfterToken[i];
35.   }
36. }
37. voidsetup() {
38.   size(250, 150);
39.   background(255);
40.   fill(0);
41.   textFont(createFont("", 12), 12);
42.   linejustify("This text should be perfectly justified.", 0, 40, width);
43. }

Okay, here's what appears to be working...
It might be a little buggy, though:

1. // justify one line of text
2. void linejustify(String s, int x, int y, int w) {
3.   // how long is the text?
4.   int tw = int(textWidth(s));
5.   // is it longer than expected width? if so, return
6.   if (tw > w) {
7.     println("Text is too long.");
8.     return;
9.   }
10.   // does it match perfectly? if so, print it
11.   if (tw == w) {
12.     text(s, x, y);
13.     return;
14.   }
15.   // if not, how much pixels shall we add to reach expected length?
16.   int gap = w - tw;
17.   // split the text into words
18.   String[] tokens = split(s, " ");
19.   // is there only one word - or no word at all? if so, print it
20.   if (tokens.length <= 1) {
21.     text(s, x, y);
22.     return;
23.   }
24.   // otherwise,
25.   // we will distribute the missing pixels after each word, in the spaces
26.   int spaces = tokens.length - 1;
27.   int[] pixelsToAddAfterToken = new int[tokens.length];
28.   for (int i = 0; i < spaces; i++) {
29.     pixelsToAddAfterToken[i] = floor(gap/spaces);
30.     if (i <= gap%spaces) pixelsToAddAfterToken[i]++;
31.   }
32.   for (int i = 0; i < tokens.length; i++) {
33.     text(tokens[i], x, y);
34.     x += textWidth(tokens[i]) + textWidth(" ") + pixelsToAddAfterToken[i];
35.   }
36. }
37. //All should be self-explanatory except leading...
38. //leading is how much room should be in-between each line of text.
39. void textJustify(String input, int x, int y, int w, int leading) {
40.   pushStyle();
41.  
42.   String[] seperatedStrings = new String[0];
43.   int lastSeperation = 0;
44.  
45.   for(int i = 0; i < input.length(); i ++) {
46.     if(textWidth(input.substring(0, i - lastSeperation)) > w * .99) {
47.       seperatedStrings = append(seperatedStrings, input.substring(lastSeperation, i));
48.       lastSeperation = i;
49.     }
50.   }
51.  
52.   if(lastSeperation < input.length()) seperatedStrings = append(seperatedStrings, input.substring(lastSeperation, input.length()));
53.  
54.   for(int i = 0; i < seperatedStrings.length; i ++) {
55.     linejustify(seperatedStrings[i], x, y + leading * i, w);
56.   }
57.  
58.   popStyle();
59. }
60. void setup() {
61.   size(250, 150);
62.   background(255);
63.   fill(0);
64.   textFont(createFont("", 12), 12);
65.   textJustify("This text should be perfectly justified. Even with two lines! You can add more text... And it still works, as far as I can tell.", 0, 40, width, 14);
66. }

Thanks for fast reply! I tried your code, and half of the text seems to disappear. I'm trying to fix that. I was also thinking of swapping every space with a non-breakable space by swapping chars in the string. The text won't be justified, but will become treated as a continuos string without spaces.

Solved the character issue by simply replacing Strings instead of Chars