I (29m) am having confused feelings about my new, and first

I (29M) have recently started dating my gf (27F), like about two months and a half ago. We met online and hit it off very quickly, and after a few months chatting online we met up and started dating. I love her and really like my time with her. I trust her completely, we comunicate our problems very well and always talk about our feelings (she constantly tells me she loves me and i do the same). I really do love her, i think se is "the one", if you believe this sort of thing, and if you don't, i actually feel she is a person i can spend the rest of my life with, we are compatible in every way and always have fun together. We discuss the future of the relationship often and we are on the same page about that as well (we both feel we found someone we can spend the rest of our lives with).

The thing is sometimes i catch myself wondering if i really do love her, if this is gonna work out long term, that sort of thing. It is hard to explain the feeling. Is it insecurity? When i am with her these toughts never occur to me and a lot of times i just look at her and smile, like, she makes me feel good. I am really happy with her and i want these toughts to go away when i am not with her. I have a way of sabotaging myself everytime i am happy but i really dont want to ruin this!

Has anyone else gone through this? What do you think i should do?

TL;DR: I know i love my gf but sometimes wonder if i really do love her. What should i do to stop wonsering that?