skyblue - I think it might work like this (assuming you are talking about jobseeker's allowance) ...
The rate of payment is calculated first - so this is 188 for you and 124.80 for your partner = 312.80
Then your household income is assessed which I assume is just your partner's earnings - if this is 380 after deductions, for the means test, 20 is deducted for each day worked up to a max of 3 days. So 380 - 60 320. Then 60% of the balance is assessed: 60% x 320 = 192.
So 312.80 - 192 = 120.80
This is all provided you have no other savings, capital, etc.
So you would lose out if you moved in together.