how does one stay positive in long distance relationship

 as a college student majoring in psych it feels very odd to be this blehhhh..im in a 2 year relationship and these few months were a bit rough mentally because i would be very iffy and sad. How does it go from seeing my partner every day when we were in HS to just boom gone꩜ .ᐟ! like how u guys stay positive and don't try to self sabotage urself???( ._. )"" i want to do better instead of being all so grouchy and let every overthinking thought take over me ,,

xoxo!>:[