listen mate i know it is hard right now, i was going out with my gf for nearly 3 and a half years, i was madly in love with her and i honestly thought we would marry one day(that normally scares the shit out of me)
she just stopped loving me,end of story,it took me a while to get my head around all of this and i stuggled to get over her though tbh when we first broke up i thought i never would.
i have since met a girl who i am having a gret a time with, so it is shows time heals all wounds.
though i have to question whetherof going away with another girl was the best plan of action to take. if she has doubts sbout your maturity that would verify them.