Welcome to HCM.
weed is not advisable as it has many side effects and is against law.
Since your boy friend is already a known asthmatic, smoking is certainly not for him as it will worsen the situation and cause him much harm.
Ask him to consult a pulmonologist
and get a chest x-ray and blood tests done and if indicated CT or MRI
scan to find out the cause for his chest pain
Wishing him all the best