Ahaha. I think Tsukasa has the potential to be bi - but the trauma of being abused has probably made him shy away from males in that sense. Girls are a lot less likely (stereotypically) to get mad and hurt him. I don't think that a relationship with a guy is impossible, but at this point trauma is probably pushing Tsukasa towards girls in that sense.
tl;dr it's complicated, I could get into why I don't think the relationship with Subaru isn't going to ultimately work out but yeah.