Tbh he doesn't sound like a shit person - and I don't think he was gaslighting you, either. It doesn't sound like he was trying to make you think you did something that you hadn't, or vice versa. Be careful about those terms - gas lighting is a really severe issue that victims of abuse go through, and I'm not really seeing any here.

I think you can definitely work through this. All relationships have problems - he was rude and disrespectful, yes, but he also doesn't display any other abusive red flags or tendencies that would have me screaming at you to run away.

I have anxiety and I've never called my partner names - I've always just said, "hey, I'm feeling pretty anxious right now, can you please chill out a little because it's stressing me out/I need a little space to breathe right now, I'll check in again with you in 2 hours" and that usually defuses the situation.

The point is that it sounds like either you're excusing his behaviour a lot because of his anxiety, or he's using it as a crutch to stand on when he lashes out if he's mad or overwhelmed. Mental health it doesn't make you a shit person, it just means you have more trouble coping with things sometimes.

If you're willing to make this work with him, you guys need to talk about emotional compromise. I'd suggest sitting down and talking through what triggers his spates of anxiety, what he needs from you and what he needs to tell you - ie, "hey, I just need some space right now, I'm feeling pretty anxious."

And you need to talk about what you need from him too. Being a widower, having a deceased ex-husband - that's big emotional baggage and probably an area that your BF doesn't have a lot of emotional experience in. If you haven't talked about it, he won't know. You do need to discuss this with him - maybe not your husband directly if that's something you don't want to share. But tell your BF how things like anniversaries and birthdays might affect you and demonstrate why you need him to be understanding about it - ie an agreement that sometimes you'll need to space out and have time to think about things, and that you'll try not to do it when you're together.