Plastic fittings present unique problems, and plastic to plastic doubles the issue.
The procedure is to tighten hand tight as far as it will go, then about 1/2 to one turn max by wrench. Any further risks deforming the soft plastic threads. There should be teflon pipe tape and/or teflon based pipe thread sealant ( dope) on the threads, and I don't see that in your picture.
Problem, of course, with glue-up is that if you need another 1/2 turn on the threads, you cannot do that without cutting something.
One other issue which is just a stab in the dark, based on the appearance of your fittings: are you SURE that the fitting screwed into the filter housing is male PIPE THREADS and not male HOSE THREADS ( both fittings are common, and the threads are different)??