Hi!! :):) I think I've had similar feelings to you, although relating to slightly different labels, so I hope this will help a little (even though I am personally still significantly confused myself!).
Don't forget that sexuality is usually a spectrum that you will likely move around on throughout your life. It can be normal to feel straight when it comes to relationships, yet still have other attraction to other genders, or think you might 'be into' other genders. It's also okay to focus your attention on the person you like/love at any given time, and I have similar feelings where I have difficulty imagining a relationship with anybody who is not the sex of the person I currently 'like' or am dating. Therefore, if it makes you feel better at the moment to focus on labels, it is completely normal to feel pansexual and be into a guy, without current romantic feelings for other genders. In the case of pansexual feelings as well, it is very possible that it is more about personality for you and that you might fall in love with anybody, if their personality is right for you. I know it seems ridiculous to say, but try not to stress too much about it. You don't always need to have a label and you don't always need to feel like you have/are the same, specific sexuality. I know how painful and confusing it can be to continuously question yourself and your changing feelings (although it is completely natural) and I'm sorry you're going through this. I don't believe there is enough sympathy out there for people who are questioning.
I personally believed completely that I was straight up until the age of 20, when I began to question whether I could ever be into people of my sex. I was always an ally but personally had no desire to ever kiss a girl and never thought that I would be able to be in a relationship with one (even after I realised I may be 'into' them). However, very surprisingly, I have been dating my current partner for a year (same sex) and I am completely in love. If someone had told me a couple of years ago that I would be dating a woman I would never have believed it (you never know where you'll be in a few years time!) It has been very hard for me and very confusing, because although it now feels right to be with her, I spent so much of my life so far being so sure that I was straight, without question.
Hopefully this made some sense to you, sorry if I've only confused you more!! Good luck :)