In English, the second degree of adjectives is formed by adding the suffix -er (except for a few irregular adjectives like good/better). Therefore, students (and native speakers) sometimes think that if something is “looser”, it should be “freer”. The fact is, however, that there is no word with three “e “s in a row in English. The simple rule is:
If you want to write three “e “s in a row in English, write only two.
This rule always applies, no matter where the three “e “s in a row would come from. For example, “freest” is “freest”, not “freest”.
However, the fact that the third “e” is not written does not change the pronunciation in this case. “Freer” and “freest” are pronounced as if they were spelled “free-er” /ˈfriːə(r)/ and “free-ist” /ˈfriːɪst/, respectively, i.e., double-syllabic.
We don’t use this rule very often for adjectives, because “free” is the only English adjective ending in -ee (ignoring words derived from it, such as “unfree”, “carefree”, etc.). However, we can see it more often in nouns.
For example, the suffix -er makes verbs into nouns. If someone skis (ski), he is a skier (skier). Similarly, a person who sees the future is a “seer”, not a “seeer”. Here, however, the pronunciation in American English differs from “free”. In British English, -eer is always pronounced /iːə/ (í-uh), but in American English “freer” is pronounced /ˈfriːər/ (frí-uhr), whereas “seer” is pronounced /siːr/ (sír), as a single syllable. The same applies to all nouns ending in -eer.