- I couldn't gush over him enough
- I can't gush over him enough
Which one is correct and why?
- I couldn't gush over him enough
- I can't gush over him enough
Which one is correct and why?
The two are equally correct based on context.
Frequently the two modal auxiliaries can and could are grouped together as a single entity. can being analyzed as present tense and could being analyzed as past tense.
So in your first sentence,
I couldn't gush over him enough
You are discussing something which happened in the past.
and in,
I can't gush over him enough
You are discussing something happening in the present.
Taken from Mithun's answer on "When do I use “can” or “could”?":
1. Ability
In the first situation, we use can with a meaning of ability. For example, "I think I can lift the box" means that the speaker thinks that she/he is able to lift the box. The past tense form of the sentence is "I thought I could lift the box".
In your case, I believe your sentence would be synonymous to "I don't have the ability to gush over him enough." You would, therefore, want to use can in this case:
"I can't gush over him enough."
It should also be noted this depends on the tense. If you are writing in past tense, you should use couldn't. I would suggest reading the question I linked above, learned something myself from the answers.