In a kind of similar position myself, stopped the regular cycling about 2000 started putting on weight about the same time too.
It really is de motivating going back out again and not been able to attack the climbs the way you used to but I always remember meeting up one ride with a really old guy, every time the road went up hill he disappeared behind me. When we met up again at the top he said ' I can climb any hill I come across I might be slow but at my own pace I can always get up'. didn't think much of it at the time but a few years and lbs later I get it, just relax and take it slow once you find your comfort zone it'll become enjoyable again.
I though this would be the year that I really get back into cycling but the weather's not helped. I never did make it up the Cat and Fidddle ( climb cose to me ) but I've kind of discovered a love hate relationship with my turbo, it can take me most of the day to build up the enthusiasm (in fact should be getting on it now but just looking for some music to listen to while riding, ha ) but once on and afterwards I really like the feeling knowing I've really done some work. look for the things you enjoy in cycling and go with it the fitness will come.
Good luck.