During adolescence, it's common to like (and not like) both people of the opposite sex and the same sex.
It may be in your nature to do so all the time, or it may be a temporary thing.
It may not be immediately clear to you which person you are attracted to, and you may waver. And that's very normal. And the changes that occur during puberty are hormones, chemicals in your body that increase and decrease. So it's common to feel happy, sad, intense emotions, and distress.
There are also anonymous phone counseling services, events, and circles where people who like the same sex (or who might like the same sex) gather. There are also anonymous phone counseling services, events, and circles where people who love the same sex (or who may love the same sex) get together. Why don't you check out the places you think you would like to talk to or visit?
Recently, some YouTubers have come out as homosexuals, and there are many books on the subject. I think it would be a good idea to gather information from these sources as well.
Like you, I once had a faint feeling for a senior of the same sex that I couldn't quite put my finger on. Your feelings are not "strange" at all.
I think it's difficult to put into words the feelings that people have for other people. Because we don't know our feelings or the feelings of others, we feel comfortable defining them with words like "I love you" or "I love you," but that "love" is not necessarily the same for ourselves as it is for others.
I don't think that you, young man, need to force yourself to answer that faintly desirable feeling you have for your senpai. I think the answer will become clearer when your body and mind become more and more mature. For now, just cherish that "I love you" feeling you have for your senpai.