Yes. In his autobiography. He also analyzed their relationship in his diaries. For some context, here's a longer passage from Ken Womack's book, Living the Beatles Legend (Chapter 31).

As January 1970 came to close, Mal began drifting into an emotional slide that had been developing over the past several years. "Seem to be losing Paul," he wrote on January 27. "Really got a stick from him today. He let me down," and ominously added "Fixing a hole," "Pepper," and "directorship" to a growing list of disappointments. Apparently, the conversation had turned yet again to the issue of Mal's servile role in Paul's life, with the roadie believing that the association was bounded by friendship and love. "A servant serves," Mal wrote, "but he who serves is not always a servant," he added, echoing John's philosophy from December 1968. "Love is as sharp and piercing as a sword, "Mal reasoned, "but as the sword edge dulls — you sharpen it. So love's keenness needs honing — needs honesty." *

[...]

On February 11, Mal joined John and Yoko for a lip-synched performance of "Instant Karma!" on Top of the Pops, with the roadie, clad in beige suit and a light-green tie, playing the tambourine. By this juncture, Mal's long-standing relationship with Paul was in freefall. A few days earlier, he have been awakened by a 1 p.m. telephone call from the Beatle. It went "something like this," he wrote in his diary:

Mal: yeah? Paul: I've got time at EMI over the weekend. Would like you to pick up some gear from the house. Mal: Great, man. That's lovely. Session at EMI?! Paul: Yes, but I don't want anyone there to make me tea. I have the family – wife and kids there. Mal: [thinking to himself] Goes my poor head, "Why????" **

By the next week, Mal found himself behind the wheel of the Apple van, moving Paul's gear from EMI Studios to Morgan Studios, another Northwest London facility where Paul could work incognito. At one point, Neil cornered Mal about Paul's surreptitious recording sessions, demanding to know more. "Where's Paul?" he asked, to which Mal tersely replied, "Not telling you."

In other instances, Mal ordered a Mellotron for Paul, while keeping him fully stocked with plectrums and other gear. In late February, Paul asked Mal to move everything back to EMI, where he was set to record "Maybe I'm Amazed" in Studio 2. For Mal, everything came to a head at 7 Cavendish Ave., when "my long love, Paul, to whom I have devoted so many years of loyalty, turned around to me and said, I don't need you anymore, Mal." *** *, ** : Evans, "Diaries." [1963—1974.] 10 vols. Malcolm Frederick Evans Archives. Entries from Jan 27 & Feb 5, 1970.

***: Evans, Mal, 'Living the Beatles Legend: Or 200 Miles to Go.' Unpublished MS, 1976. Malcolm Frederick Evans Archives.

Each key has magnetic tapes, individually. The length of the tapes are 3/8. The mellotron has sounds like brass, woodwind, and string instruments. Specifically the flute, violin, and trumpet. It also has choir sounds. The tapes have 3 tracks, A, B, and C. This allows the sounds to be played individually. The sounds can be played together, this is by the rhythm selection. You mixed between the different instrument sounds. It also has a playback head and has a pinch wheel that presses the tape strip against the rotating rod. This is by pressing down on a key. When you press a key, it allows you 8 seconds of a note. The 35 set of keys, range from G to F. The right side allows you to play the lead instruments. The buttons are above the keys to select a track for sounds to come out on the mellotron. There are knobs to switch between sounds on the track you select, you can also control the volume and adjust the pitch.

I explained about the mellotron the best way I can 🙏🏾💫.

Musicians will either love or hate this particular keyboard, sometimes it can get confusing. I think the instrument is quite mysterious yet versatile.

As I call it the wondrous mellotron.

Picture some rooks hanging out indoors, playing a relaxing card game, and it's about to rain outside. This EP's kinda hard to describe. It blurs the lines between, surf, lofi study beats, garage rock, shoegaze, and emo, if you care to try and categorize it.

Mellotron Demo