If some one left you for the no good reason, You should not get tense and get into depression, That person wasn't meant to be with you, Just let him go and move on. If someone loves you , he/she will never left you, It shows the person who left you doesn't love you at all. He/she was with you only for some greed. You plant are your friends, as you have said, your mental life effecting them and they are not doing good due to this, You need to do more focus towards them and everything will be okay.