Sensibly merging two dataframes

If one of my dataframes gives me some info about items:

    itemId     property_1      property_2     property_n       Decision
 0      i1          88.90             NaN              0              1
 1      i2          87.09    7.653800e+06              0              0
 2      i3          78.90    7.623800e+06              1              1
 3      i4          93.02             NaN              1              0
 ...

And the other one gives me some info about how users interacted with the items:

     userId        itemId      Decision
  0      u1            i1             0
  1      u1            i2             1
  2      u2            i1             1
  3      u2            i3             0
  4      u2            i4             1
  5      u3            i5             0
    ...

I am interested in predicting the Decision, which is easy to do if I work with each dataframe, separately. But can I somehow incorporate the second one into the first one, given that in the second one, each item appears multiple times with different Decisions?

I would like to have something like:

    itemId     property_1      property_2     property_n     u1_decision  ...    Decision
  0     i1          88.90             NaN              0               0               1
  1     i2          87.09    7.653800e+06              0               1               0
  2     i3          78.90    7.623800e+06              1             NaN               1
  4     i4          93.02             NaN              1             NaN               0  
   ...

So each user becomes a column, result in something very sparse. The first question would be whether this makes sense, and the second question would be how do I merge the rows from the second dataframe as columns into the first one (I know how to df.merge on Decision, but this doesn't give me the desired result).