Learn Italian: Sei risentito, infatti ce l'hai ancora con me! - You are resentful; in fact, you're still angry with me!

This comes from the pronominal verb avercela con qualcuno, which means "to be angry with someone" or "to have it in for someone." In ce l'hai, ce is the pronoun ci (changing to ce before another pronoun), l' is the pronoun la (referring to a vague "it" or the situation), and hai is "you have."

Why does la drop its vowel to become l' in ce l'hai?

The pronoun la elides to l' because the verb form hai starts with a silent 'h' followed by a vowel. In highly common expressions like avercela, the contracted spelling ce l'hai (just like ce l'ho or ce l'ha) is totally fixed and always used.

Does infatti act exactly like "in fact" does in English?

It is similar, but Italian uses infatti strictly to confirm or give evidence for the previous statement. In English, we sometimes use "in fact" to introduce a contradiction, but here, the anger (ce l'hai con me) is the direct proof of the resentment (sei risentito).

Is risentito related to the basic verb sentire?

Yes, it is the past participle of risentirsi, meaning "to take offense" or "to feel resentful." While sentire means "to feel," adding the prefix ri- and making it reflexive shifts the meaning to feeling slighted or bitter. Here it acts as an adjective.