How do you know if your girlfriend really loves you?

I would suggest asking her honestly and openly how she feels about you and your relationship.

If that prospect is too intimidating, you can try to think on it and figure it out yourself.

Does she say she loves you? Does she ever say it first, or only in response to you saying that you love her? If she says it first, without your prompting, this expression of love is more likely to be genuine.

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I would suggest asking her honestly and openly how she feels about you and your relationship.

If that prospect is too intimidating, you can try to think on it and figure it out yourself.

Does she say she loves you? Does she ever say it first, or only in response to you saying that you love her? If she says it first, without your prompting, this expression of love is more likely to be genuine.

When you spend time together, do you only do things that she likes to do, or do you also do activities that you like to do? If you only do things she likes to do, she may not really value your interests. 

Do you know her friends and family? If so, do you spend time around them together, or only in passing? If she feels really comfortable with you, she will likely enjoy spending time with you and her friends or family in the same setting.

Does she call or text you first or only in response to your messages?

Does she do favors for you? Like wishing you a good day, writing you little messages, giving gifts? If so, does she expect you to reciprocate? When someone loves another person, they like to do favors to make that person happy without the expectation of something in return. 

Love means something different to everyone. I recommend you look into the "Love Languages" and try to find out what yours and hers may be. If she tries to communicate with you in her "love language," I think this may mean she loves you.