OK, I only skimmed the other posts, so I hope I'm not being repetitive.
I saw two big issues. 1) "You can't expect me to be supportive unless you tell me ahead of time what your goal was." 2) "He wants me to lose weight."
Regarding #1: What the heck?!?!?! No. Just, no. I'm sorry, maybe I'm wrong here, but if you are happy about achieving something,
he should be happy for you. The fact that he is putting conditions on when he'll be supportive is just insane. And very, very worrisome about what that means on a larger scale. I would have told him, "My goal is weight loss. Anything that shows an achievement of that counts." Seriously, it does. And he should celebrate every single achievement with you.
So, in order to show support or praise, you must first specifically state that it is a goal? Man, I'd be such a smart-hiney about this. "I'm sorry honey, I would have told you that you did a good job with the bbq tonight, but as you didn't tell me that was your goal, I can't." "I can't tell you that your hair cut looks good. You didn't tell me that was your goal." "I'd praise you for getting us through that traffic nightmare, but you didn't tell me that was your goal."
Regarding #2: It seriously sounds like he is way too concerned with you losing weight. He really, really shouldn't care that much that you be skinnier. He should be supportive and helpful, not critical and judgemental. And he's being judgemental. Have you asked him, how would he feel if you
gained weight? Would he still love you? I HOPE so, but seriously, this post makes me concerned that this question may be necessary to ask.
So, I totally agree that he is insecure. This is 100% some issue with himself. But it's kind of beside the fact, because this is toxic to you. I don't think this is just an issue of "don't talk about it" or ignore it, don't seek his approval. This is a cancer in your relationship. You're going to have to confront him about this and have a real conversation on the matter. Hopefully you can frame it in a good light, without accusations or more toxicity. But you may have to ask tough questions. And, please keep in mind the possibility that this could be a symptom of a bigger issue.
Maybe it is part of his marine mentality, that instead of praising what you achieve, he should push you (however roughly) to do more. You need to make him understand that this just isn't going to work for you.
Good luck!

I truly believe anything can be bettered with the right conversation.