I'm really hoping this question will be helpful for others, as well.

I'd like to think that I'm a pretty positive person and try to see the best in people, but I am also pretty sensitive, take things too personally, and have trouble managing my emotions. I literally have to force myself to take a time-out from communicating (because yes, I feel like a child) with my SO to prevent my upset self from saying something I'll regret later, but if the trigger of whatever it is that sets me off happens in person and not remotely, it is hard to use this time-out strategy.

My SO has pointed out, rather delicately, that I am overly optimistic about things (which he likes about me), but that sometimes I don't think everything through (true) and I take things too personally when things don't work out (true). I think he's right- I'm overly optimistic, a bit impulsive, and then because I'm so optimistic, when things don't work out I become very disappointed and that effects my mood and general effort to be a "goddess of fun and light." He has anxiety and adhd, so it is absolutely crucial that I stay understanding, positive, and supportive.

So the typical pattern is that I will get really excited about something (I plan a date, he hypes up a date he has planned, he says we're going to have the best week ever when his roommates are out of town, etc.), and then when it doesn't work out (he doesn't like my date, he cancels his date- for a legitimate reason, he makes other plans multiple times the week he hypes up and doesn't hit me up until after dinner time), I will be overcome with disappointment. I think these feelings come out of an insecurity that I'm not good enough for him or that I'm not important enough for him. The thing is, we hang out daily, he emotionally supports me, he does things like move me out of my apartment, goes on trips with me, and all of these other great things and I really believe he's a great captain. But then I get upset about the smallest things. For example, recently I got really excited about an evening where he hyped up us eating dinner in his bed and watching a movie. When I called him, he said he'd be ready in a couple of hours. A couple of hours later when I texted to see whatsup, he said he had just had dinner with a friend and was debating whether or not to go to the gym. Honestly I want to be the person he feels comfortable bailing on, and I did a good job at not getting immediately snippy since it was by text but it came up later when I eventually went over to his house and I was a bit snappy. Would it have been better in that situation to not go over if I wasn't completely over it, or would that have made a bigger deal out of something small?

If I'm away from him, I can usually convince myself not to say anything, and then reflect and become understanding that he is a busy person and has good intentions. I also like the time to think up something clear and concise before telling him. However, I'm not nearly as good if we are talking on the phone or in person and something sets me off, as my disappointment and hurt feelings become so much stronger than my ability to control them, and I clam up and can't find something positive to say.

I am also bad at staying positive when I think he is upset or mad, and this makes things worse. I want to cheer him up, but sometimes he is just, for whatever reason, not having it and I feel inadequate in making him happy. Then I get in a sour mood, which makes me snappier.

TL;DR: Tips on controlling your emotions in the immediate moment? Does literally biting your tongue work? Pouring coconut oil in your mouth? How to prevent yourself from catching a contagious negativity?