I don't think you necessarily have two personalities (mind, I'm not an expert). I don't think there is anything wrong to having a serious side to your nature - it happens as we get older, 30 is a great age to be IMO, young enough to have great fun and enjoy like we do in our early 20's but old enough to have a serious take on life - as we have to in order to progress further career/life wise. I'm sorry to hear you suffer depression, but maybe you're reading too much into this. I believe we all change our views, opinions etc as we age - I'm 42 now, and I've changed so much since I was 30 in my views, interests etc but I'm still the same fun loving person underneath. I hope I don't sound patronising, as I said I'm not an expert it's just my opinion :-)