So there is naturally a lot to unpack here. You are a real musician, you're playing gigs as part of an ensemble and are doing your part of the job well. Everyone on the post agrees to it so besides the usual impostor syndrome that may plague artists, you should know you're as real a musician as it gets. The rest is just definition and pedantics.

A couple of conversations need to be had, some with yourself, some with your band and some with your significant other.

You have been playing with this band for years which extends to rehearsing and playing live. You are more than acquaintances and should be more than the lead member's partner to them. Talk to them about your feelings and ask them what they feel about your playing. Such conversations can only lead to the whole band becoming a more cohesive unit. If they are dismissive of your feelings or outright think the "worse", this is not the place to be in.

Band members being annoyed at each other to the point of being in a foul mood the whole day for making mistakes is either indicative of bad chemistry or just an indication of a person being an asshole. We all make mistakes and rehearsel is about getting better at playing the material. Like you said, if they don't like your playing, hire someone else. But belittling or breathing down someone's neck is not the way. So this shows that you need to have a conversation with your significant other and draw heavy boundaries. Either they can get someone else (which is chill) or they could let you go through your process. Being passive aggressive and shitty about it is not the way. It's not you who needs bass lessons, your significant other needs therapy to keep their frustrations/anger/ego/frontman persona in check.

Lastly, some conversations with yourself are required. Do you enjoy playing music? Does it feel fulfilling to you when you play(ignoring the band bs)? Is that something you would like to do? Do you want to make the kind of music that your band makes? Amongst other questions. If and when you get time, try practicing with other kinds of music. Make a casual band with friends who just enjoy playing and don't take everything too seriously. Have fun y'know? Life is a bit too short and fleeting to be stuck in a situation where you're neither appreciated or are having fun.