Chris and Jill want each other so badly but neither of them will make the first move. It was even questioned in Revelations whether or not they are going out or not, because Jessica wanted to jump Chris's bones and ride him but he didn't even pick up on the hints etc.
Jill and Chris will become a couple eventually.
Leon and Ada love each other though but most of it was foreplay in Resident Evil 4 but they got into an intimate kiss with Ada in Resident Evil 2 when Ada supposedly died in Leons arms.
Not sure if Claire shared the same feelings towards Steve or perhaps she did.
But I can see Sherry and Jake falling in love. And the TC is probably right and it may just happen.