<human>: I (**24M**) meet my girlfriend (**25F**) in high school, we became really close friends. After three years of being practically best friends I asked her out, she was hesitant at first but then said yes. At the time I was 20 and she was 21. First few months were amazing, I thought I was in love. But I was not sure, she was the FIRST girlfriend I ever had. We've been together for almost 4 years and live together. The first time we said the L word was the first time we were having sex. I heard it and I said it back, only to find out a little later from her that she didn't say it first. She had thought I said it and I had thought she said it so we just repeated what we thought we heard, which was 'I Love you.' So pretty much an accidental 'I Love You' and we've just been saying it ever since.

So lately I have been having doubts about our relationship. I know it's bad, but I have been thinking about breaking up with her just to see what else is out there. I have never dated another girl or even flirted with another girl besides my girlfriend. She has had two other guys in her life, one in high school and a fling with a married guy. For the most part our relationship is good, we hardly fight, but lately I've just been not caring and just going along with the motions. I mean I care about her, I would do anything for her, and I want her to be happy, but I feel the same way about everyone I care about.

Every time she tells me she loves me I just repeat it. She always tells me 'why you never say it first?,' and that is my problem. How do you know you still love someone? Is the spark gone? What should I do?

Can you condense the text into a few key points?
<bot>: Having doubts about 4 year relationship, not sure if I'm in love, and getting an urge to date other people. Is the first person sometimes the right person?