as much as i believe you can headcanon whatever you like i really think that the idea that till secretly was also in love with ivan the whole time but was in denial about it or didnt realize it kind of detracts from their story
till doesn't have any reason to be in denial about his feelings, he just simply doesn't feel the same. he wasn't raised in an environment that would give him any reason to have internalized homophobia. nothing would change if ivan was a girl. he just doesn't love him back.
but looking at any of the supplementary material like the beach scene art COUGH or any official actor or student AU stuff shows that maybe, in another life. till could have loved ivan. if the two of them were raised in a different environment and met and lived under different circumstances, they could have been in love. in another life. in another universe.
but in the world of alien stage, it was never going to be that way. and that's what makes it all the more tragic.