Conor McGregor Showers Fiancée Dee Devlin With Gifts For Birthday

Conor McGregor spared no expense for Dee Devlin's birthday this week ... putting on an epic boat party for his fiancée, while showering her with designer gifts.

The UFC superstar shared pics of his surprise bash for his lover on Tuesday -- one day before Devlin, who's pregnant with the couple's fourth child, officially turns 36 -- and you can see, the guy went absolutely all out.

McGregor strung up a ton of balloons -- some pink, some gold -- in a room on their yacht ... and then he forked over handbags and shoes that cost several thousand dollars each.

One of the gifts was a super rare Chanel purse ... which the fighter said had significant meaning to him, 'cause it represented his big feelings for her.

"Baby my love for you is as deep as the ocean!" McGregor said of the presents and the party. "Here is the limited edition ocean @chanelofficial bag, among other things you love!"

"I love you baby," he added, "happy birthday ❤️"

The lovebombing didn't stop there ... 'cause the couple and their kids eventually hit one of the boat's decks for a big cake!!

The two have been nearly inseparable since McGregor was accused of sexual misconduct at an NBA game back in June -- she traveled to New York to give him some TLC just after the allegations surfaced ... before they jetted off to France earlier this month for a vacation.