Indulge was first recorded in 1630–40; from Latin indulgēre "to give free reign to, to be lenient toward, to accede, to take pleasure in."  The verb: indulge; 3rd person present: indulges; past tense: indulged; past participle: indulged; gerund or present participle: indulging. 

The verb "indulge" first appeared in the English language in the mid-17th century, specifically in the 1630s.  The Oxford English Dictionary earliest evidence for indulge (verb) is 1638, indulged (adj.) is 1682, indulgence (noun) is 1362, indulgence (verb) is 1599 (in the writing of Thomas Nashe, writer), and indulgent (adj.) is 1509.  Merriam-Webster records the first known use of indulge as circa 1623. 

Examples of "indulge" used in a sentence: 
"The soccer fans indulged their patriotism, waving flags and singing songs." 
"I love champagne but I don't often indulge myself.
"We took a deliberate decision to indulge in a little nostalgia."  
"I don't indulge in idle gossip"
"Since she retired, she's been able to indulge a growing passion for literature." 
"The chocolaty sweetness in this zucchini loaf makes it perfect for the indulging dieter and fussy eater alike."  
"The menu was quite extensive, and the indulging father let his children order whatever they wanted."

Just the facts:

INDULGE Definition & Meaning - Merriam-Webster

INDULGE Synonyms: 79 Similar and Opposite Words | Merriam-Webster Thesaurus