Tim has never had a steady girlfriend - he's much too afraid of [a] commitment(s).

"commitment" (uncountable) is fine.

"'commitments" would not be wrong, but I would leave it as it is.

You have typed a hyphen where you need a dash. Many people do this in informal writing because the dash can be a nuisance to type. (Many people also do not understand that there is a difference.) In careful writing you should use proper dashes though.

GPYYou have typed a hyphen where you need a dash. Many people do this in informal writing because the dash can be a nuisance to type.

Entering the proper dash is particularly inconvenient in answering or creating posts in EF's text editor, but not impossible.
- (hyphen)
– (en dash)
— (em dash)

Regarding 'commitment' - thanks, so I will leave it as it is.

Regarding the hyphen and dash - I didn't know there is a difference, but I have just googled it (for example, there should be two en-dashes above) and now I know the general rules about using both (or three of them actually). Unfortunately my keyboard does not allow me to type in a dash easily...
Do American keyboards have

In the EF editor, you have to click on the "Insert special character" tool, and from there you can pick all sorts of symbols and characters not found on a standard keyboard.

A small comment.
Some people feel that dashes are often over-used, and that they should be avoided in formal writing.

eg Instead of

Tim has never had a steady girlfriend - he's much too afraid of commitment.
one could write
Tim has never had a steady girlfriend. He's much too afraid of commitment.
or
Tim has never had a steady girlfrien

You can also type dashes by pressing the ALT key and then either 0150 – (en dash) or 0151 — (em dash) on the number keypad. I use them fairly often and this is actually very quick if you have a keyboard with the number keyboard to the side.

It's a bit trickier on a laptop, because you have to use the function key to access the number keypad, but ALT plus FN and then the numbers will work

AlpheccaStars, as you said, not the most convenient way but it works. Thanks

Clive, did you mean that all fo

Yes.

It is amazing how many new things I have learnt on this forum thanks to people that voluntarily help. Thank you all so much!

CliveSome people feel that dashes are often over-used, and that they should be avoided in formal writing.

I agree that dashes should not be overused, but not that they should be avoided in formal writing. My opinion is that dashes, when used correctly, are fine in any level of English.