I'll start off with your second question, because it sounds like the less complicated one to answer.
Would it be accurate? People have different perspectives on what the Tarot is (is it some sort of spiritual thing? Is it much more mundane than that?) but even if you're looking at it from the divination angle, it sounds like it could be inaccurate or, at the very least, easy to interpret incorrectly.
A good guideline of Tarot is to not ask questions you're very personally interested in, especially if you're starting out. Nobody's going to go to your house and take away your deck and your membership to this forum if you do. In fact, I'm sure plenty of us did or do this. Nevertheless, it's still probably wise to keep in mind why people often use that guideline to begin with.
If you ask a question about something you're personally involved with, you probably have a specific outcome that you wish for. Even if you're not doing it intentionally, it's very easy to end up projecting, and seeing what you want to see on the cards. It could very well happen that a reading could tell you that he felt a friendly sort of affection to you and you could believe he's in love with you, or he could be in love with you but if that seems too implausible you may end up assuming it's just friendliness.
Is it ethical? If you believe that the Tarot can give you any real answers about his feelings, then I would say it's about as ethical as snooping through his Facebook messages or stealing his mail. Which means, not very.
Regardless of whether it would work or not, it's not a very good start to any relationship if you resort to means other than direct communication to try to find out information that he's kept private from you.
If it didn't work or if you interpreted it incorrectly, you could end up making matters worse. If it worked, it still wouldn't tell you exactly what to do with that information.
If you need some guidance and want to resort to the Tarot for that, I suggest making your questions about things you can do something about and which are about you. What can you do to improve communication? How can you improve your self-confidence (if you feel too shy or nervous to talk to him about it)? What would be the best way to approach the subject? Are there any clues you're missing that you should pay attention to because they're good signs or red flags?
Something like that puts the focus on you and your actions. It helps you think about what you can do on your end. If he doesn't feel the same way, there isn't a lot you can do. If he's causing problems in your relationship and being hurtful to you, then at least you'll have a clear conscience from knowing you've done your part and he didn't do his. It's also important that you're able to know what's most emotionally healthy for you (and him) and whether those problems are a sign you should fight on or simply choose your battles and find someone else who may be more compatible with you. Ultimately, that's what matters, that you were able to analyse your behaviour, fix any flaws, and be honest if the problem isn't you.