What I'm going to say about this man...
Actually no not that. I want to mention that Doomguy has consistently shown more emotion / shown emotions with more depth, at a more intimate level when he is with other MEN.
Or male-presenting characters.
Doomguy acted the most naturally when he was with animals. But we can't deny the substantiality put into every time him and Valen interact. We had him pause mid-action, and then save Vega the queer sentient AI in 2016, and not to mention the Intern. Even in the codex he was described to sacrifice himself to save the Night Sentinels who saw him as a true-born warrior and their brother. Back when they couldn't put detailed expressions on him, and we could still feel the relationships he had with other male allies are flavorful and layered, through nothing but his body languages. Only exception is Samur, but hate is a different kind of emotional intimacy.
And now behold, the obvious care and concern he had towards Marok, before and after he fought him:
Look into the first gif, how much of his resolve was shaken by worry. The subtle quivering of his pupils. He lifted his eyebrows as a telltale sign of sympathy. He unclenched his jaw and unpursed his lips to soften his facial expression, as he became open to help the boy.
Did I mention the Wretch/Architect? Every time those two interact you just feel like you are witnessing something you shouldn't.
To give in to overanalysis.
The leg is the longest limb of one's body, kicking Samur with it creates a distance, which is a clear sign of "Not wanting anything to do with someone". Likewise, Doomguy has been consistently keeping his contact with thira non-existent, giving her his back 4 times, once turning while she was talking to him, and his hands are working, completely disengaged with the supposed conversation. During the "save the princess" scene, he paused mid-action, only to avoid her hand (important point later), chose a spot very much away from it, and used only two fingers to make contact. Such choices of body language are actively creating distances, they are indications of a lack of interest and refusal to engage beyond necessary.
On the other hand, every time Commander Valen and Doom Slayer met face the face, their fingers are almost always brushing. Once when Valen was handing him the Celestial locator and they had a little tug of war. The other when he was resurrected and Valen handed him his helmet. After everything that had happened and all the disagreement they had with each other's actions, they still felt comfortable with each other's proximity.
For a nonverbal character, Doomguy is extremely hands-on. Every hand movement and where he places his hand is very intentionally animated to explicitly tell the player about what's going on in his mind as well as the subtext of a scene. E.g. The part where he slowly pulled out the doomblade to finish Samur off, showing he is conflicted.
And then there's the Wretch:
I think the Marok boss fight did awesome job storytelling. It really shown that Doom Slayer never went for the kills like he used to. Despite how ANGRY he was at the boy, he didn't want to hurt him. The only thing on his mind was how to save Marok. Every "phase" ended with Marok temporarily gaining back consciousness before being re-tethered. He punched and choked Marok with those powerful hands that can certainly break neck if he wanted to, but he just wanted to get the latter out of control or knock him out. Some teeth may have fallen, but no major damage was done. Marok was only collapsing from the overexertion, looking confused and terrified. And this is his first expression. Immediately choosing mercy.
The arena was surrounded by the same black smoke as in the flashback. Then the explosion triggered his ptsd so bad he hallucinated that little girl again. Marok is the little girl, but this time he realized he really couldn't do anything about it, and he has made peace with himself.
The Wretch/Architect is a completely different story.
He was smiling (Everyone pay attention the Doom Slayer is SMILING oh my god) at him. But there is also sorrow in his eyes because he could foresee the future where they part ways, perhaps even become enemies. But for now, His darkest truth was laid bare in front of this creature, and Architect finally decided to not hide from him anymore, and although the key was destroyed, everything was okay after all. Perhaps for the first time ever in the entire Doom timeline he let his guard down and trusting entirely, you could see how tender his eyes are. It's 2026 and Doomguy is doing the gay yearning.
After the praetor suit was made he returned to this guarded look. But those eyes are still saying so much. How much he is going to miss this place and the person he meet here. He knows what he has to do and who he is now, but still it's hard not to miss when he was taken care of and and someone who fully understood the extent of his wounds. Also he is very comfortable with Architect dressing him up, relaxed with every touch. They've spent some time together and you know he will carry it with him physically into his eternal war against Hell.
I'm not saying he's gay I'm saying he's not straight. At the very least he seemed to have zero chemistry with women of this world but All of it. Dialed to the maximum with the guys. Sorry. Guess that's just the way it is with Doom.
As a joke comparison this is his face in front of a female ally:
Probably sulking cuz he thought he was about to join Valen's search party...