I mean, I could see writing this as a funny Valentine's, but that is in context of my own partner and I.

You seem to have already had conversations about sincerity, and from my own perspective I wouldn't say this is sincere. I mean, it's just references to sex.

I don't think it's a malicious card, like he wrote it just to upset you, but it is thoughtless in the context of your previous conversations with him. Communicate you feelings about this to him, and his reaction will tell you what to do.

But, also take this with a grain of salt. I ain't no relationship expert, just a potato on the internet.