What does this even mean? We'd have a great time but I see us as just friends?

I (31m) asked a girl (24f) on a date and she said "We'd have a really great time but I see us as just friends". She's shown a lot of interest in me in the past with flirting and eye contact and me the same but she had a boyfriend. They broke up, got back together and broke up again, and I found out from a mutual friend she was on dating apps so I asked her on a date and she said that. I don't understand because it's like she's saying "we'd have a great time but I can't". If she's single and she'd have a great time I don't know why she would kind of reject the date unless it's because I'm older, she's not ready (she's on apps?), she doesn't like me that way or her friends advised her not to. She's my younger cousins best friend and we know the same kind of social circle through my younger (female) cousin. All the signs she gave when we've met in the past in social outings have been that she likes me and I even had people say to me afterwards "why was she looking at you like that, is something going on?". Nothing was, but a couple of other people noticed the eye contact from her when we were looking at each other and smiling across the room.

I get the feeling she has some reservations because my age, my status i. e maybe she thinks I'm a player (I'm not) or I'm not serious about her but now it's fizzled out and we haven't spoken since. I kind of replied and just said thanks for the honesty, I like you and if you change your mind let me know.

I don't know if she thinks I just meant one date and that's it, or whether I was trying to just hook-up. I don't know. I haven't spoken to her friend , my cousin about it and nobody has mentioned it but I haven't seen anyone since.

What does this even mean? We'd have a great time but I see us as just friends?
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