Thanks for your question. I'm happy to help you today.
There are a few, relatively common reasons that you might be feeling this way - but these are just my initial reactions upon reading your question, so feel free to reply to this message if there are considerations/factors involved that you'd like to share with me. The first thing that comes to mind is that you start to feel smothered in your relationship - regardless of how much you really love your partner, sometimes, people just need a bit of space to feel like their own person again. A lot of couples spend all of their free time together, and you might start to feel like you want to do some things on your own (see your friends, go for a walk, whatever it is that you did
when you were single). It doesn't mean you don't love your partner, it means that everyone needs time alone, and perhaps you're not getting enough of that. So if you feel guilty, for example, for wanting to spend time away from your partner, you might start feeling irritable and start snapping, although you don't mean to act this way - because you might feel bad about wanting space for a little while. It's not uncommon - a lot of men need to "retreat" for a short period of time, regroup and just spend time on their own. You say space doesn't help - but you also say you feel like you need distance, so those are two statements that indicate to me that you are just feeling conflicted, perhaps, about your own needs.
The other possibilities are that you feel troubled by certain aspects of your relationship - perhaps your partner has unresolved issues and leans on you for support, perhaps a bit too much. Sometimes, people start to feel irritable in relationships when they feel compelled to meet all of their partners needs, even though it's not very realistic to have the expectation that you are solely responsible for your partner's needs. Maybe your partner has some things going on in her life that need to be dealt with but she is ignoring them or not handling them the way you feel like she should. Or maybe she has the expectation that you are supposed to "handle it."
Sometimes, if you feel this way for a long period of time and can't quite put your finger on exactly what's going on, couples counseling (or individual counseling) can help you get to the root of the problem/issue. If you feel like that's something you'd be interested in, you can find a counselor in your area on this website:
I hope that helps. Please let me know if you have any further questions.