I'm sorry about your son's dad.
It's hard to give advice about this kind of thing on here, because we don't know your son's general health, what kind of support he's getting (a psychologist, a therapist, your family's pastor or priest or other religious leader, for example?).
Who has suggested medication? A teen psychiatrist who deals with grief counseling will be the best person to consult. A psychiatrist is able to prescribe meds if they're necessary, whereas a psychologist or therapist is not able to prescribe meds.
A psychiatrist, because he or she is a medical doctor, will also be able to gauge your son's general health. If your son is not taking part in activities, is not eating well, is not socializing, is not getting some fresh air and exercise, for example, the doctor will be able to address all these concerns. He or she may refer your son to a support group, or suggest that your son take karate lessons, take steps to improve his own situation through eating better or walking daily or journaling, or whatever is needed to help your son deal with his very difficult and challenging situation. He or she may refer your son to a family doctor for an assessment of his electrolytes or other blood levels, along with his general health condition, in order to make the best psychiatric medication recommendation.
Medications depend on the person's weight, lifestyle, ability to comply with instructions, medical conditions, etc.
My best piece of advice, after years of experience with a teen - now a young adult - who has been on multiple medications, including antidepressants, anti-anxiety meds, etc., is to develop a good relationship with one pharmacist. Believe me when I say that the pharmacist can be your best ally.
A pharmacist who is regularly available, whether he or she works in a small pharmacy or a major chain pharmacy, can help you immensely. The doctor may say "take one of these a day" but the pharmacist will tell you "don't take these with this food or this drink" or "make sure to take these at the exact same hour every day" or "you'll notice this at first but it will decrease" or "it might take 3 weeks to take full effect" or "no, your son should not take that because he also takes _____, so let me call the doctor and discuss a safer alternative", or "that's a perfectly normal side effect and it's harmless" or "stop taking it immediately and get to the ER". I've encountered all those and more. Get on board with a good pharmacist and ask questions.
I hope your son gets the help he needs.