Hello Jude,
I know just what you mean about enjoying yourself when you are out, but finding it hard to actually get out there.
Looking back, I'm sure I've been doing that "I'd rather stay at home" thing since childhood, on and off...I used to refuse invitations to go out, even as a teenager, just because it felt too stressful to think about getting ready and then facing it all out there... And then I'd be miserable at home, feeling left out and as if everyone else was living a more exciting life.
I manage to out to go to work: no choice there, of course, but even so I get quite depressed on Sundays as it looms up again. And at the end of my working week I'm so relieved to be back home and be able to stay there (where it's "safe"!) for a while! But I know that this reliance on "home" isn't healthy for me: I use it as a place to hide from the real world, and it's a bit like my relationship with food: I use it for a "comfort", though I know overeating leads to me feeling unhappy.
I have to resist that pull to stay home all the time...often when my husband wants me to go shopping, or to the pub, with him I have to force myself out. One of the worst is not going to the gym, which I totally need to do for my physical and mental health, but over and over again I find a reason not to go: always some other crucial job that needs doing...at home, of course!!
When I do manage to go, and thankfully (largely thanks to all of you on this site!) at the moment I have started to go again, (nearly as often as I should...) I still have to say to myself, as the excuses start to emerge in my mind.. "Just GO!". And I have this little conversation with my reluctant self, whenever it starts to try to wriggle out of going, "Just GO, just GO"...and so I do, grabbing everything quickly and getting out the door before I can change my mind! I'm very clever at finding really plausible reasons for staying, but I try not to listen to myself!
And then of course I'm pleased I've gone. Don't know if a similar little trick might work for you Jude.
Good luck with getting out there! Love, Sarajo.