Welcome to HCM,
I appreciate your feeling about your partner,his chest congestion and coughing may be due to irritation of smoking
to fungus or pollens or viral infection.
But fact remains there smoking is definitly detrimental to health,there are many many heath hazards of smoking.
You can always suggest to quit but he has to agree to quit smoking.
As you know nicotine
is addictive we always keep on saying quit smoking ,I am sure explain him and he will certainly give it a thought.
If required you can take help from professionals to help him to quit smoking.
Best of Luck