Should I tell my boyfriend I m having suicidal thoughts?

YES , young lady... you should tell him... especially given the fact he's aware of your medical past...
but far more critically important is to immediately let your closest available family and your Family Doctor there as well- exactly know what you're going through ...
ask for and timely get the help you need....
it sounds to me you urgently need the professional help of a psychiatrist -in real life- in your area, someone skilled in treating people of your age, with no further delay...due to your suicidal thoughts...
consider getting AT ONCE to the Emergency Room inasmuch as you feel that bad...yeah....
please, understand, heed and act by the fact that your life and quality of life are holy enough shrines to thoroughly be protected - whatever it takes....
stick to life... timely get the help you need...
and may life come your way....
may you brightly overcome your life's hardships...
may you make all your dreams come true...
the best possible, dignified way...
here-in this world...
may you stay forever- blessed and kept safe and proof from all harm

It would be more wise to tell a doctor.