it’s horrible when people just end relationships with no reason, i’ve been there. you will for sure spend lots of time thinking “why” or “what if…” but the main thing you need to remember is that it’s their issue, not yours. you did your best, loved, and now deserve to heal properly. go through the grief and grow with it, cry as much as you need and allow yourself to feel that sadness. however, unless you think it’s strictly necessary for your process, don’t reach out to them to ask why. sometimes the answer you’re seeking has already been given to you simply by their lack of explanation (and at some point even respect).