<human>: Condense the text into a few key points

Hello.
We've started dating more than 4 years ago, live together about 3 years.
I care for her, I want her to be happy, I am accustomed to her, but I don't really know if I love her. 

There were good and bad times but I didn't question my feelings in them.

However, there were bad times (2-3 month) recently when I thought I must endure - she wrote her PhD in great stress - she had panic attacks at night, she cried every other day because she thought she'll fail (there were circumstances that made her to be in hurry - she really could not postpone her PhD), she snapped at me etc. I supported her, but after this I felt tired and felt no strong feelings towards her. I thought it is OK, there are ups and downs. But then I met a girl that took my mind for 2-3 days. I am thinking about her, despite the fact that I don't really know her - I had only one 10-15 minutes talk not about work.

Even before these hard times I was not sure if I want to marry her (there were time I thought I was, though, but I did not want to hurry because I am young and was afraid).

And here I am doubting if I still love my gf. For those who had LR and lived together - how do you know if you still love your partner?
<bot>: been together for a long time, not sure if I still love her. How do you know if you're still in love? How some of you knew that it was time to end it?