This may be responsive to a medication such as viagra
. However, a full medical would be important as there may be a medical or psychological cause for the erectile problems. I would advise you try to get him to see his doctor for a discussion. Reassure him that this is a very common problem (I dont know your partners age but in the older age groups it is an easily rectifiable probelm).
In the meantime, you may wish to explore non-penetrative sex
, oral and manual stimulation if these are things you are comfortable with.