My SO has been very unhappy with himself and his progression professionally. He's getting progressively more responsibility and pay, certainly enough for what I'd hope from him, but not nearly enough by his own standards/timeline.

He's talked a lot with male friends about his frustrations but seems to turn inwards and spiral into depression around me. He doesn't want to talk much and what I have said (that I think he's capable and respectable and that I admire his ambition) seems to have made things worse...

How can I best support him?

We usually talk on the phone for a little bit before bed and see each other on most weekends.