Neither lambda nor nu

For the causative, I like mu.

O kea ta se si mu loha ni se?
ABL=what TOPIC 2SG=PERF=CAUS=love 1SG 2SG
"Why did you make me love you?"

or, periphrastically,

O kea ta se si mei ko ni loha se?
ABL=what TOPIC 2SG=PERF=cause COMP=1SG=love 2SG
"Why did you make me love you?"

(Not sure if o kea is going to be "why" -- just calquing from Polish for a sec for example sentence fodder.)

There could also be various other options for the periphrastic type of operation, along the lines of English make, let, help, force, compel, ask, &c.