I agree with Leed in that its not healthy to become too involved in your friends business and get concerned when they can't always get back to you quickly. People have their own lives to deal with and sometimes frequent messaging isn't possible. If they are experiencing difficulties like suicidal ideation let them know you are there to support them and discuss things should they wish - maybe send them some links or some numbers for a crisis line but other than that let them come to you. After you're not a professional, its down to this person to decide how to proceed in regards to their mental health. Im sure they're greatful just to have you there to listen and offer advice when you can. In the meantime i would focus on your studies and other stuff you enjoy. Hope ive been helpful teebs, see you around on chat ok?