According to their website, here's the difference between knowing you're in love and just thinking that you are:
1. If You Think about the Other Person Constantly, You’re in Love. if Thoughts Come and Go, You Think You’re in Love
You can't get the man you love out of your head, no matter what you do.
2. If You’re Selfless, You’re in Love. if You’re Using Your Partner to Fulfill Your Desires, You Think You’re in Love
You should be trying your best to make your partner happy, not to be making yourself happy.
3. If You Willingly Make Sacrifices, You’re in Love. if You Don’t Want to Change for Someone else, You Think You’re in Love
You'd try your hardest to become a better person if you were really in love. Otherwise, you wouldn't waste your time.
4. If You Aren’t Forcing Things, You’re in Love. if You Find Yourself Making Too Much of an Effort, You Think You’re in Love
Relationships require effort, but loving him shouldn't be an effort. You can't force feelings.
5. If You Feel Unconditional Affection for Your Partner, You’re in Love. If His or Her Quirks Bother You, You Think You’re in Love
Everyone has negative traits. However, when you're in love, you won't mind those traits.
6. If You Think You’re in Love, You’re Not in Love
When you're truly in love, you don't have to think about it. You'll just know it.