Long term Relation

How can I establish a long term relation with a one of the Demons from the Arts Goetia . Is this accomplished through a pact ? Because I want to work with one of them on a long term basis , not just once off

Start by evoking them (or invoking, whatever you prefer) and start the conversation. Ask them questions, get help and see how your energies gel with each other. After you’ve done that a few times and the entity starts to feel familiar to you, then it’s much like any relationship, you start to know each other and you know if you want to get more serious.

At that point, Ask the entity if they’d be interested in a pact. Have a clear purpose for the pact, even if it’s for a lifelong effort to be the best you can be, know what you’re doing together. If they say yes (they don’t always) then perform a ritual to dedicate yourself to the pact and you both sign it.