I think a lot of people after 20 or more years of use probably experience the same thing you do, Addictedforyears. The whole thing of having the friends who you used to smoke with quit and you feel left behind, so you still sneak around in order to get the smoke. Think of it this way. If you quit, you'll be able to hang out with some of those friends again, and you'll find your relationships have depth to them without the smoking.
Right now I'm 27 (been smoking since 15 with only a month's break or so here and there, never any longer than that), so a few of my friends still smoke. I'm wondering how many of us will still be smoking in our 30's and onward. I will say that the group of my still-smoking friends is dwindling as a few more of them quit every year. I just don't want to get left behind I guess. I don't want to be hanging out and feeling like I have to leave early so I can go get blazed.
Unlike your stereotypical situation with stoners, I haven't befriended people based on our habit alone. I have to have more in common and a deeper connection with someone than our drug of choice to call them my friend. Also my best female friend is a non-stoner and has never even tried it. Sorry, I'm kind of rambling off topic here, but I just wanted to illustrate that those connections you had may still be there without the weed.
Since you're about to become a parent, I'd say quitting soon or now would be your best bet. Your son or daughter will have a more present parent if you're not stoned (I say this as a kid who had a perpetually stoned dad). Also, if some of your ex-stoner friends also have kids, there's another excuse to get together with them so you can socialize with them and your kids can all play together. Actually some of my best childhood memories are of my mom and stepdad's friends coming over with their kids (who also became my friends). Think of how cool that could be.
I wish you the best of luck. Check out the "Best of Quitters Wisdom" threads. They are excellent and I'm finding even more inspiration in them. It's definitely not going to be easy after 20 years, but I think it will be worth it. I'm in the process of cutting down this week by only taking a couple of hits every night (and waiting until as late as possible to do it), and then giving my "accessories" away to a new home on Friday night - too broke to buy new implements for smoking should I be tempted, so I'm thinking giving the stuff away will be a good way to ensure I don't backtrack (and I've asked the person I am giving them to NOT to give them back to me no matter what, even if I ask). Saturday is going to be my first day sober since my last attempt at quitting about 6 months ago. I'm done marinating in resin and coughing up phlegm when I'm not even sick. I'm sick of the groggy, fog feeling when it wears off and having to refresh it. I would continue writing the list of "cons" about being a stoner, and you may find in time that it highly outweighs the "pros" especially as you get older. That being said, you have to do it in your own time.
I thought I could be a "treat smoker" too. Each time I've tried quitting, it's been the "treat smoke" that's gotten me back into buying a bag for myself and going right back into the daily habit. I would love to be one of those people who could just smoke a few times a year or whatever, but I just can't. I have finally come to that conclusion. I'm not saying that'll be you, but after 20 years you may have to just forego it, even as a treat. That being said, I think the feelings of a natural high just from enjoying life may actually be better once you've been quit for awhile!
Peace, love, and good luck! Keep reading and posting. I've been reading the posts here for a couple of weeks while mulling over my decision to quit for good, then I just joined a few days ago. In that short time, this forum and the people on it have been a great motivator for me. Hopefully this can be a helpful place for you, too!