<human>: Could you distill the essence of the text into 1-3 sentences?

We have been together for a year and a half. I am here first proper boyfriend and she put her trust in me. I do love her but I feel I am no longer in love with her. She has been away for the whole summer and she asked me about going before hand and if it would change things between us, I said it wouldn't, thinking it wouldn't.

We have made promises to each other for life commitment and kids etc, I realise now these are promises I shouldn't of made as how could I know how I would feel in the future? 

Since she has gone and from a bit before she went I have been having these feelings/thoughts. Nearly every hot girl I see I feel like I want to fuck her/approach her and chat but I can't because I am in a relationship, I want to be a free man again. I feel like I am too young to be in a committed relationship for the rest of my life, I have a problem with having only this one sexual partner for the rest of my life. I want to have some more partners and not another long term relationship for another say 10 years. I like being by myself which is another thing, sometimes I get annoyed when I dont get time to myself. I have actually been enjoying my time to myself while she has been away.

So she is back in a month and sure I can't stay in this relationship, I don't want to end it while she is there as she will be devastated when If I do it and I don't want to ruin her trip. I want to know the best way to let her down gently. This has to happen as if I am having these feelings now, if I stay, how will I feel in 10 years let alone the rest of my life. I feel it is best to break up now rather than let it be even worse in the future. I know she will be sad but at the end of the day it is my feelings that matter to me and I know I won't be happy staying in the relationship. 

So, what is the best way to explain this to her without her being too hurt?
Thanks
<bot>: in a committed LTR of 1.5 years and feel I no longer want to be in it for the rest of my life. What is the best way to let her down gently?