I just wanted to share a similar experience that I've had as well. I actually had been getting a few messages from a group and it was super random things, The only way I was able to resolve the matter was to find out who the original sender was an block their phone number with my provider. I hope this may help with you situation as well.
Odd question, does your boyfriend use a signature on his phone? Any change if he disables it? Can I ask if you guys are on different carriers?
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