My boyfriend caught me smoking a few nights ago, which wouldn’t have been an issue if I had told him that I smoked. The reason I didn’t is I had quit months before we began dating. When he caught me, I had just been tempted by a friend smoking, and simply took a few puffs. Now, he thinks I have been lying about my habits and who I am. I have even asked friends of mine to tell him that it was just a few puffs, and that I had really quit, but he looks at me with a deep suspicion that I can’t get him to shake. I think this is starting to be a little childish because I’m not lying. If he can’t handle this, it should be his problem and not mine. Am I wrong to think this way?
You’re not wrong but being patient with this may help more than being belligerent. You have been honest and don’t have to apologise for anything, but this is his problem for a reason. It may be less about the act of smoking and more about not knowing something about you that is troubling him. Give him some time to get used to the idea that you’re an adult who can make your own decisions. If he doesn’t get over it, and still can’t trust you after a prolonged period of time, that’s when you should be more alarmed.

How can we slow things down in our relationship without me coming across as a problem? My boyfriend loves me and wants things to get serious, but I am more cautious and like to take my time. How do we find a balance that works?
Being clear about your individual expectations is the best way, because it avoids misunderstandings and allows you both to move towards the future with your eyes wide open. Tell him why this relationship is important, and why you need time. If he wants it to work, he should have no problem accepting that.