What makes you say 'I love you' to a woman?

Today I was told twice by a guy that he loves me.
Although it seemed more of a friendly kind of 'I love you,' I joked 'yeah, I can see that,' but he repeated himself saying 'but I do love you'.
How serious do I take this remark? Is it just a general sense of comfort that he's making me aware of?
I felt it was quite odd to be told so randomly.
The two of us are just friendly and as far as I'm aware, he's seeing someone.
What makes you say 'I love you' to a woman?
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