Face it, you're set in your ways. You've been living alone for years, and you've become accustomed to not having to accommodate anyone but yourself. This doesn't mean a happy, healthy relationship isn't possible for you. It just means that you might have to pause now and then to consider your actions and reactions as you wade into a new lifestyle.
Ditch the Baggage
In one respect, starting a new relationship after a long time alone can be a lot like getting involved again right away – it's still your first relationship after a bad one, so a lot of the same concerns apply. Although it's possible that you parted ways with your ex with an amicable handshake, you might be carrying some unresolved emotional baggage. Try your best to leave your old relationship behind, preferably behind a locked mental door. It's human nature to react to past mistakes and to try to get things right next time, but don't overdo it. Your new partner isn't your ex, so you can't atone for past mistakes and you can't hold her responsible, even subconsciously, for past hurts. Don't be so afraid to lose again that you hold on too tightly and lose track of yourself – that person you've spent years on your own getting to know.
Accept that the cap on the toothpaste matters again. Whether you’re inherently sloppy or painfully neat, you've had your own way with everything around your house for a long time. Unless you've discovered your clone, that's probably about to end. When your new partner begins spending significant time under your roof, loosen up with a few of your more stringent household rules, if necessary – or tighten them and try a little harder if your new partner is a neat freak. This applies to the big things too, like the fact that you always go to the mountains in July, but she's not one for roughing it. Try something new that you both might enjoy, maybe something neither of you ever considered before.
You probably didn't live in a monastery all those years you were alone, nor did your new partner. If you're still traveling in the same circles, it's inevitable that you'll eventually cross paths with someone you casually dated before. Tackle the problem in advance, if possible. Get word out that you're seeing someone new and that it might be serious, so if you take your new partner to your old hangout, someone you dated a few years ago won't unwittingly throw herself into your arms for a big sloppy kiss. Give some thought to how you're going to feel when you run into one of your partner's old flames as well. If it causes problems that you're hanging out with your single friends four nights a week just like you used to, you might want to cut it back to a night or two – particularly if your new partner isn't overly fond of your single friends. It's not an all-or-nothing situation, or, at least, it shouldn't be. If she doesn't want you to see your old friends ever again, this should give you a moment's pause.
Opposites attract, but flashing sparks don't necessarily make for the best long-term relationships. Unless you're particularly resilient and adaptable to change, your first serious relationship after a long time alone might be more successful if you match up with someone you have a great deal in common with. Getting involved again is a big change in itself. If your new partner is diametrically opposed to everything you believe in and is your polar opposite, this presents a double challenge.