It’s a tricky one. Do I think Enjolras returns Grantaires feelings when we are first introduced to Les Amis? No. It says in the text that he disdains him, and that Grantaire is an ‘unaccepted Pylades’ – something that obviously will come up later in the text.
Do I think Enjolras hates Grantaire? Absolutely not. Disdain is far from hate, and he never sends him away even though it’s clear he has the unspoken authority in the group to do so. The fact he decides (grudgingly) to trust Grantaire with Barriere Du Maine speaks volumes about the fact that maybe he has hope for him, and would like Grantaire to prove himself to the group – and to him.
Do I think it’s still unrequited by the time we get to their death scene? No. The transformation in Grantaire and the title of the chapter referencing Orestes and Pylades says everything – Grantaire is no longer an ‘unaccepted Pylades’. Enjolras has accepted him for that role; ergo, he returns his affections, even if sadly only briefly and even if in a way that’s up to debate. Because really, it’s not a sudden revolutionary passion that has transfigured Grantaire, it’s his love for Enjolras.
So yeah. I personally think it’s a bit of both.