Travis Kelce sure sounds like a guy who's in love ... 'cause he just raved over his relationship with Taylor Swift -- straight-up admitting he "couldn't be happier."

Stephen A. Smith grilled the Kansas City Chiefs superstar on his feelings for his girlfriend for several minutes during a recent sit-down on "The Stephen A. Smith Show" ... check out some of the 35-year-old tight end's answers -- he certainly seems smitten.

Kelce told the ESPN analyst he and Swift are "in a strong relationship" ... and because of it, he's "as focused as I've ever been on my job."

"I'm enjoying all aspects of life," Kelce said with a smile. "That's for damn sure, man. Me and Taylor are happy and I couldn't be happier to have that confidence and that comfort off the field, and all the support I could ever ask for in the stadium, man."

Kelce actually said the love he feels from the popstar is one of the biggest reasons he tried to make it out to as many "Eras Tour" shows as he could last year.

He told Stephen he wanted her to feel just as supported in her craft as she made him feel about his.

As for her thoughts on the future of his playing career, Kelce made it clear she doesn't want him to retire anytime soon ... even if his numbers have dipped a bit this season.

"She loves coming to Arrowhead and coming to the games and cheering for me," he said. "So I've got all the support in the world to keep chasing these dreams."

As for her career, Kelce obviously doesn't want new music to stop coming any time soon ... revealing he is "the No. 1 Swiftie!!"