I believe
it is more of a 'because-it's-5-years-relationship' that
contributed largely to this great reluctance to drop the
relationship. This relationship is probably akin to a drunken
stupor, running on marginal consciousness despite experiencing
little growth.
Your relationship is merely being pulled along by sheer force - the
moment anyone of you stop pulling it, your Love will perish with
immediate effect.
Already, as it seemed to me, there are signs of a mutual desire in
wanting out, but is hindered apparently for some unspoken reason/s.
You have found someone comfortable and she has found what she wants
in life - then, shouldn't the both of you pursue what you two
reckoned that could provide the happiness each of you seek?
Without growth in relationship, often, there's little to look
forward in Love.
Time change & people change; therefore needs change. True Love
might be a constant, but our needs change as our inner self
develops. Love may stay, but needs change because our Self
condition will not remain forever in the same state as it did five
years ago.
Surely there are reasons why you two ended up together five years
back, but when we spiritually and emotionally start to evolve
subconsciously - what that began the same,
might one day diverge and grow differently.
Because Love is truly not about looking at each other, but in one
collective direction. The minute the relationship loses this
vision, it loses its soul to function.
Perhaps you might want to discuss with her if there is a
possibility of this shared vision and how you want your
relationship to move in the future. If there isn't a common goal,
then perhaps, it might be beneficial for the both of you to come to
a mutual agreement to null this relationship and end this
amicably.
Why delay the inevitable? Reminded me of a Chinese Proverb - liu zi
wu yong, qi zi ke xi (Mundane to keep, but pity to throw).
You don't have many 'five years more' to consider - especially your
girlfriend. 
Cheers
