This answer may surprise you if you're not too familiar with gmg dynamics, because you would think on a surface level that the answer would be Tr but nope! I've answered a similar question before and the conclusion is still the same: it's Ricky.

If we rewind all the way back to k-con Hong Kong, you'' find a moment where Gw is asked if he could be any member for a day which member would it be? Mttw looks all smug and happy thinking it will be him but then the POUT. Mttw's beak comes out and he looks soooo mopey lol oh if only I could've been a fly on the wall to see how Mttw reacted afterwards to the Saju reading when the fortune-teller said Rk & Gw were complimentary because of the moist earth thing kshdfksdjfhkuh the way gyubrik and geonmaet got effectively swapped and the fact that Gw even COMMENTED ON IT is so 😭😭😭 anyways sorry I'm getting side tracked...

I think bc Rk is objectively a Super Attractive Dude and also can be very gentle and introverted, sometimes Mttw can't help but feel a little jealous. In a kind of inferior complex way, not in a mean not-wanting-them-there-or-to-spend-time-together way, but just because Rk is a totally different genre of person to Mttw and just a whole different vibe altogether. I think Gw is probably a bit different in his behaviour towards Rk (more settled, less chaotic) and that may occasionally make Mttw feel a bit like "oh why can't he be like that with me?" or "why can't he see me that way?" BUT! Again these are my own personal guesses and complete headcanons. Pls do not take my words too seriously, I just enjoy these theoretical thought experiments!!