saintpeta - maybe there is a sort of compromise you can reach. I am afraid I recognise some of myself in your DH. My wife is much more like you (but would stil hate going on any kind of holiday with others).
Me and my wife have come to a compromise (as per frumpygrumpy) and we are both happy about it.
The first rule we have is that my wife organises all social events. She has total control over the calendar and I go with whatever she wants even if I do not feel totally happy.
The second rule is that she has some old friends that she likes to see in London and I encourage her to go and I look after the kids, clean the house and make her generally feel welcome when she comes home and talk to her about all the conversations she has had. I do not socilaise on my own with anyone and all my friends are also friends of my wife except a few of my ex students.
The third rule is that my wife knows there are some things I hate so she does not push them at me. For example as flibertygibet say about her DH my idea of hell is a school Quiz Night or indeed any school function where I have to interact with people I do not really have anything in common with.
We have quite a few close friends and I think I am a nice person who likes people and when I actually get to a party I enjoy them. It is really the whole build up and the arranging of social occasisons which is the worst part for me. I used to hate work parties for similar reasons.
It is possible that if your DH could screw up his courage a little bit and you are really supportive of him and go to a few low key social functions together he would actually enjoy them when he got there. The more he does it the better he will feel. I know it worked for me but it took a long time and lot of love from my wife and I am eternally grateful to her.
2rebecca - I agree with pretty much everything you say. Socialising is an over rated passtime. Being on your own (or with just a few close friends) doing hobbies is a good thing as well if you like that way of life.
Sorry I could not name check everyone else - there are lots of good comments on this thread.