Hi Lillypup, it's always hard dealing with an adult child who needs help. The fact that he's working and going to school sounds like he's pretty high functioning so it may be that you've caught his issue early.
I guess you have two routes:
1) tough love--if his living at home or you are financially supporting him, you can make medication and seeing a therapist a requirement for continued support. That's so hard--it tears you up, it may damage your relationship for a very long time, and you have to be prepared to follow through and actually cut him off. Hard on him and you. If he were having more issues and really struggling with day to day living, or if you feared he was suicidal, it might be easier to take this path. It's up to you on whether the positives outweigh the negatives
2) Gentle love--is ghete someone whose opinion he respects that he might listen to if they spoke to him about taking meds? Maybe try that approach? If not, is he willing to try more "natural" approaches like SAM E, high dose vitamin D, talk therapy with a therapist? Fischer Wallace also makes For Use at home device that runs a very mild current (generated by a little battery so it's hardly anything at all) through a headband you wear for 20 minutes 2/day that has some research showing it does help with depression, anxiety and insomnia. Might he be willing to try something like this?
Again, only you can decide how hard you want to push your son. Whatever you decide, I'm sending thoughts of peace of mind and strength your way. I've been in your shoes and it was hard. But it was harder to watch my daughter suffer