Small gestures.

I love it when he brings me a cup of tea randomly - I didn't ask for it but he made it me anyway because he thought of me in that moment.

Or when they bring up certain info they've clearly memorised about you up now and then.

Only people who care for you will do this.

I dont know anymore. Everytime I thought or I felt I was loved romantically, I figured out that it wasn't true. In my personal experience, people seem to use those 3 words easily. It's like they think it's time to say it or that I'm expecting to hear them and they want to meet those expectations. Don't take me wrong, who doesn't want to hear from the person you love that they love you back? But jeez, do it only if you really feel it. Don't lie bc that's heartbreaking at the end. Smh.

The way someone looks at me, for sure.

If the person sends me an "I love you" or something like that on WhatsApp

IMO, what LaDamaX said. Though I guess some people may have doubts even when somebody loves them because of past experiences of being used, or other reasons like low self-esteem. Notwithstanding any of that, I guess if you have to ask if yourself if s/o loves you, that may be a sign/red flag?

The person tells you, their actions support their words, and you feel it/sense it.

When they refrain from lighting me on fire and throwing me out a window, that's when I know it's for real, wifey material right there 😭

When the loving person tells me. Anything else can be self deception.