The short answer is that you find out by asking him and then watching what the following month does with his answer, and I know that is not the answer you came for, because if asking felt possible you would not be typing how to know if he loves you into a search bar at this hour. So I want to spend most of this on the reason asking feels impossible, since that is where the real question lives.
What I will not do is give you a way around him. No sign, no card and no article can tell you what another person feels, and the sites that offer to are guessing with your hope. What I can do is help you find the question underneath this one, which is usually smaller and more answerable than the one you typed.
The question behind the question
When somebody writes to me with this, and I ask what they would do with a yes, the conversation nearly always turns out to be about something else. Sometimes it is am I allowed to want more than I am getting. Sometimes it is did I imagine the first six months. Quite often it is if I ask and the answer is no, what happens to my Tuesday evenings and my sense of myself, and that one is the heaviest because it has nothing to do with him.
Those questions are yours, and you can work on them without his cooperation. The fear of asking is nearly always the fear of what you would have to do next, and once you know what you would do next, the asking gets lighter, because the answer stops being the end of something and becomes a choice between two next steps.
How to know if he loves you without decoding him
People who are afraid to ask do a great deal of reading instead. They read the gaps between messages, the way he said fine, whether he used your name, the photograph he liked and the one he did not. I have done it myself, and I can tell you that the reading gets more skilled and less accurate the longer it goes on, because you are interpreting a person who has not been asked to explain himself.
There are things you can observe without interpreting, and I have written about the ones that hold up in signs he loves you. Broadly, they are the ones that cost him something and were not announced, and you find them in what he does over a month rather than in what he says in an evening. But observation only gets you to a strong guess, and a strong guess is exactly what you have already, which is why you are still awake.
What to ask him, and when
Ask in daylight, not at the end of a night out and not at the end of a fight, and ask when there is somewhere for both of you to go afterward, a walk or the shops, so the answer does not have to be sat in. The plain question is fine. Do you love me is a sentence people manage to say on a kitchen floor, and it works better than any of the clever versions.
Then listen for the second sentence rather than the first. The first sentence is usually the one he thinks you want, and the second one, the one that starts with but, or with I think, or with the truth is, is his. If there is no second sentence, ask one more question, and make it a small one with a picture in it: when you think about next summer, am I in it. That question cannot be answered with fine, and its answer is something you can hold.
What to do with the answer
If it is a yes, you are not finished, and I say that kindly. This is the part of how to know if he loves you that the lists leave out. A yes is a sentence, and the thing you were actually missing is the evidence, so the useful move is to notice over the next month whether the days start agreeing with the sentence, or whether you find yourself back here in six weeks with the same question and a new set of screenshots. If you are back, the yes was real and it was not enough, and that is a thing you are allowed to say to him.
If it is a no, or a not sure, or the long silence that means the same thing, then you have lost an evening and got back your whole attention, and you will be sad, and the sadness will be about something that was actually there rather than about a story you were keeping alive on your own. Almost everyone I have heard from who asked says afterward that the asking was the smaller pain. Nobody I have heard from says they wish they had waited another year.
If you are afraid to ask
Then the fear is the finding, and it deserves a slow look before anything else happens. You have boiled the kettle twice tonight and made nothing, and I would guess the question has been sitting on the counter for weeks while you walked around it. A question that could end things has not ended them by being asked. It has only shown you what was already true, a few months earlier than you would otherwise have found out.
If the fear is bigger than that, if you are frightened of how he would react rather than of what he would say, that is a different kind of fear and it is not one an article can hold on its own; a counselor or a helpline is the right size for it. The does he love me page draws three cards for the version of this that is about your own side, and it will not report on his feelings, because it cannot.
What is worth doing today
Today, write the exact question you would ask him in one sentence in your notes app, in the words you would actually use, and read it out loud once in an empty room. Do not send it and do not schedule it. Just hear which word you stumble on, because the word you stumble on is usually the one that has been keeping you from asking, and knowing that makes tomorrow’s version shorter. If you want company while you work up to it, how to know if he is the one asks the longer questions, for when this one has been answered.
Come back and tell me which word it was.
Clara