If you've been an asshole to yourself for long time, don't worry. Change takes time, but it's totally possible and eventually automatic. Here are a couple quick ways to get started:
- Be brutally honest about whether your expectations are realistic. Would you expect the same thing from a friend who feels the same way you do now?
- Avoid using distractions to take your mind off your thoughts, and give yourself permission to think and feel whatever you're thinking and feeling. Even if it's uncomfortable.
- Tell yourself what you might say to a friend in the same position -- if you're a good friend, you wouldn't be an asshole
- Remember that inadequacy/anxiety/frustration/rejection/etc. are common, and there are millions of others going through a similar experience
Take up a (free!) hobby that encourages self-reflection
Without knowing your emotions, habits, triggers, automatic reactions, and so on, you're destined to have nasty fights with your partner and to raid the fridge whenever you feel... anything at all, really.
So how do you get to know yourself outside of therapy? If you're a Google employee, your company handbook requires you to know this, but for everyone else, mindfulness is an easy, straightforward way to begin.
Don't worry, it's not as touchy-feely as it sounds. All it means is paying more attention to the present moment, i.e., stop checking your damn phone. The easiest avenues to this skill are contemplative practices: sitting meditation, or moving meditations like yoga, tai chi, qi gong, and walking meditations are a few ways. You can also try journaling, and thanks to modern technology, you don't have to do it in a skull-and-crossbone-decorated notebook labeled "NOT FOR PARENTS." I like to open a Gmail draft email, address it to no one, and write. Sometimes I go back to it, but most of the time I don't. It's a password-protected, automatically saved way of getting to know yourself better.