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

Okay so a little back ground.
Me [m21] and my girlfriend have been together on and off since 2011.  I can't remember every reason we split but I feel like it was mostly my fault. We recently got back together a few months ago and things are well I guess.

 I'm having thoughts that maybe I keep getting back with her because I feel like I won't be able to feel how I feel about her for anyone else. Or that I'm scared of being alone, she keeps bringing up the subject of getting married and I don't want to get married. She knows this as I tell her every time.

 I feel like either we want different things in life or that maybe I don't feel how I think I do about her. I wouldn't question any of this if I did right?

Also I feel like I have so much invested into this relationship that I'm stuck in a way. Back in 2012 she was pregnant and had a miscarriage. Then in 2013 again but it implanted on the outside of her fallopian tubes? And she had to get an abortion as the doctor said it had low chance of survival and could harmful to her as well. 
Weve always been there for each other and we tell each other we love each other everyday. I've also recently started therapy for depression and anxiety but after a while I feel like i think these things more and more.

 I don't know what to do, or what to think and I figure I'd post here to see aome other opinions. Feel free to ask me anything and ill try my best to answer your questions as this means a lot to me.
<bot>: Having second thoughts about a decently long term relationship and don't know how to feel emotionally and asking for advice/opinions.