[emphasis mine]
No it isn't.
I would say it is.
Does some girl you fancy reciprocate the feeling to the extent of actually loving you? Only you can answer that question
to your satisfaction.
Since it is your satisfaction that is paramount (to you), no one else can dictate standards for you.
Your girlfriend does the girlfriend thing with you, but also does the same with one or two other guys. Or she bases her "love" on specific conditions, material or otherwise. Or her love is lukewarm, not passionate.
So is this truly love? And basis this love, will you continue on a relationship with her, or even ask her to marry you? Only you can decide that.
I may, basis my standards, offer you advice, if I were your friend. But I cannot impose my standards on you.
Does she love you, your girlfriend? Love you enough for you to act on? Only you can decide that. (And it is you that must live with the consequences of your decision, for better or for worse.)
With evidence, obviously. I disagree with David Mo when he says no evidence comes into play here. But how much evidence is enough, that is subjective, only you can decide that.
(With an equal amount of emphasis as you put in.)
Or are you someone who takes a poll of your friends, a peer review as it were, to decide whether your girlfriend loves you, and whether you should ask her to marry you, basis that evaluation? Even if you do that, it is still subjective, except you're voluntarily abdicating your decision, your standards, in favor of someone else's standards.
eta: Generic "you", needless to say. No personalization intended.