Phone texting random new number

Yesterday night I was arguing with my boyfriend (Android user) over text and instead of replying I deleted the entire text thread we had going instead of replying in a snarky tone. It was probably months worth of messages. this morning I finally text him and someone answers “who’s this”

obviously I was baffled as to why my bf of many years would even say that . So I continue texting thru out the day and get a message that says “go harass someone else”

I messaged him via email to ask if he had blocked me or something and he said no. He said he never got my messages . So I look under his contact card and his number is there but also some random new number below his. I check my service providers records online and I’ve been texting some random number . How is it possible a new number was added to his contact card and that none of my messages went to him and instead a random number I’ve never ever seen. I googled the number and it’s from a few towns away. This has happened before . Where I delete his entire text thread and then when I text , someone else replies saying it’s not him but indeed a different number that has no reason to be under my boyfriends contact number . This happened as well when I deleted the entire text thread, it started texting someone else’s number that is nowhere on my phone .